Foundation of Java Programming

JGuru · Sep 25, 2016

Foundation of Java Programming

This is guide for learning Java programming for budding programmers & those who are beginning Java programming.
These are very introductory programs (beginner to intermediate level).
In order to become a very good programmer you need to be

1) Very good in logical reasoning (problem solving skills)

2) In depth knowledge of Java API (Application Programming Interface)

So let's get started !!

Q) Write a program to list the contents of a directory ?

Ans) To list the contents of a directory , use the java.io.File class Use the file.list() method.

List.java

Code:

import java.io.File;
import java.util.Date;

// List the current files in the directory similar to Windows console
public class List {

    String path = ".";
    File directory = new File(path);
    String[] content;
    File file;
    String fileName;

    public List() {
        // Get the current directory contents
        content = directory.list();
        for (int i = 0; i < content.length; i++) {
            fileName = content[i];
            file = new File(fileName);
            //If it's a file
            if (file.isFile()) {
                System.out.println("" + new Date(file.lastModified()) + "       " + file.length() + " " + fileName);
            } else {
              //It's a directory
                System.out.println("" + new Date(file.lastModified()) + "   " + "<DIR>   " + " " + fileName);
            }
        }
    }

    public static void main(String[] args) {
        new List();
    }
}

This program the contents of a directory . It prints the last modified (Time) , Size of the file, filename.
If it's a directory we display the <DIR> . We use the directory.list() method to get the list of files in the current directory.
The condition file.isFile() is true if it's a file, otherwise it's a directory!

Q) Write a program to display the Size of the directory in MB or GB also count the number of files & directories ?

Code:

import java.io.File;
import java.text.NumberFormat;

public class GetDirSize {

    private int fileCount = 0;// Count the number of files
    private int dirCount = 0;// Count the number of directories
    private long fileSize = 0;
    private NumberFormat nFormat = NumberFormat.getInstance(); // To format the Numbers

    public GetDirSize(String directory) {
        System.out.println("Calculating, Please wait...");
        long dirSize = traverseDirectory(new File(directory));
        if (dirSize > 1000) {
            // Represent it in GB
            System.out.println("Size of the Directory : " + (double) dirSize / 1024 + " GB");
        } else {
            // Represent it in MB
            System.out.println("Size of the Directory : " + dirSize + " MB");
        }
        System.out.println(" No of Files = " + nFormat.format(fileCount) + ", No of Directories = " + nFormat.format(dirCount));
    }

    // Process the directory contents
    public long traverseDirectory(File dir) {
        if (dir != null) {
            //If it'a a directory
            if (dir.isDirectory()) {
                dirCount++;// Increment the count by 1
                // Get the files & directories of the directory
                String[] children = dir.list();
                if (children != null) {
                    for (int i = 0; i < children.length; i++) {
                        traverseDirectory(new File(dir, children[i]));
                    }
                }

            } else {
                // It's a File
                fileCount++; //// Increment the count by 1
                fileSize += dir.length(); // Accumulate the file size (bytes)
            }
        }
        //457 MB = 47,95,62,693 bytes
        //479562693 bytes -> 457 MB
        // ?
        return (fileSize * 457) / 479562693;
    }

    public static void main(String[] args) {
        if (args.length > 0) {
            new GetDirSize(args[0]);
        } else {
            // If no argument is specified, use the current directory
            new GetDirSize(".");
        }
    }
}

To run the program type the following from the cmd-line

java GetDirSize D:/

If the path contains spaces , use double quotes.

For eg.,
java GetDirSize "D:\Documents3\JSession\My Programs"

Here we use a method called traverseDirectory() that traverses the entire directory to get the directory size, no. of files & directories.
We increment the directory count by 1 every time we find a directory, else we increment the file count by 1. We get the size of a File using
the method length(). We keep accumulating it until we traverse the directory.
And finally display the size of the directory. Also display the no. of files & directories.

Q) Write a progtram to list the contents of a directory recursively?

Ans)

Code:

import java.io.File;

public class TraverseDirectory {

    public TraverseDirectory(String path) {
        visitAllDirsAndFiles(new File(path));
    }

    public static void main(String[] args) {
        if (args.length > 0) {
            new TraverseDirectory(args[0]);
        } else {
            //Show the contents of the current directory
            new TraverseDirectory(".");
        }
    }

    // Process all files and directories under dir
    public static void visitAllDirsAndFiles(File dir) {
        if (dir != null) {
            if (dir.isDirectory()) {
                System.out.println(" <DIR> " + dir.getName());
                String[] children = dir.list();
                for (int i = 0; i < children.length; i++) {
                    visitAllDirsAndFiles(new File(dir, children[i]));
                }
            } else {
                System.out.println("   " + dir.getName());
            }
        }
    }
}

To run the program

java TraverseDirectory <path>

For eg.,

java TraverseDirectory D:/

If you don't specify any path then the current directory contents are displayed.

Here we define a method called visitAllDirsAndFiles() that takes a File as argument and processes it.
It uses recursion to display the contents of the directory. Recursion is a simple & effective technique in
programming to solve some problems. Some problems like directory listing, Factorial lend themselves well in
recursion.

Q) Write a progtram to list the contents of a directory recursively using the wildcard pattern?

If the wildcard pattern is "*.java" then only Java files & directories must be displayed.
Accept the path & wildcard as cmd-line argument.

Ans)

Code:

import java.io.File;

public class TraverseDirectory2 {

    static String wildCard = "";
    int dotIndex = -1;

    public TraverseDirectory2(String path, String wildcard) {
        wildCard = wildcard;
        dotIndex = wildcard.lastIndexOf(".");
        if (dotIndex > -1) {
            // Get the last name ie., jpg from *.jpg
            wildCard = wildCard.substring(dotIndex + 1);
        }
        visitAllDirsAndFiles(new File(path));
    }

    public static void main(String[] args) {
        if (args.length > 0) {
            if (args.length == 1) {
                new TraverseDirectory2(args[0], "");
            } else {
                new TraverseDirectory2(args[0], args[1]);
            }
        } else {
            //Show the contents of the current directory
            new TraverseDirectory2(".", "");
        }
    }

    // Process all files and directories under directory
    public static void visitAllDirsAndFiles(File file) {
        if (file != null) {
            if (file.isDirectory()) {
                System.out.println(" <DIR> " + file.getName());
                String[] children = file.list();
                for (int i = 0; i < children.length; i++) {
                    visitAllDirsAndFiles(new File(file, children[i]));
                }
            } else {
                if (wildCard.equals("")) {
                    System.out.println("   " + file.getName());
                } else {
                    if (file.getName().endsWith(wildCard)) {
                        System.out.println("   " + file.getName());
                    }
                }
            }
        }
    }
}

To run the program type :

java TraverseDirectory2 <path> <wildcard>

For eg., java TraverseDirectory2 "." "*.java"

Will list the directories & Java files in the current directory.

Q) Write a program to count the number of Words & characters in a String?

Code:

// A program to count the words & characters in a String
public class CountWordsChars {

    String str = "Java is a great programming language";
    int charCount = 0; // To count the number of characters
    int wordCount = 0; // To count the number of words

    public CountWordsChars() {
        System.out.println("Word Count = " + count(str) + ", Charaters = " + charCount);
    }

    // Return the number of words found also count the no. of chars
    public int count(String string) {

        if (string != null) {
            //Convert the String to char array
            char[] charArray = string.toCharArray();
            char c;
            for (int i = 0; i < charArray.length; i++) {
                //Fetch every character (char)
                c = charArray[i];
                if (Character.isLetter(c)) {
                    //If the character is a alphabet
                    charCount++;
                }
                if (Character.isWhitespace(c)) {
                    // If it's a whitespace (' ')
                    wordCount++; // Increment the word count by 1
                }
            }
            // At last we increment the wordCount by 1
            return ++wordCount;
        }
        return 0;
    }

    public static void main(String[] args) {
        new CountWordsChars();
    }
}

Here in this program we declare a method called count() that take a String as argument and finds the number of words in a String,
as well the characters in a String.

Q) Write a program to print the prime numbers from 1 to 100000 ?

Ans)

Code:

public class Prime {

    int MAX = 100000;

    public Prime() {
        for (int i = 0; i < MAX; i++) {
            if (isPrime(i)) {
                System.out.print(i + " ");
            }
        }
    }

    // Checks whether a number is prime or not
    public boolean isPrime(int n) {
        for (int i = 2; i < n / 2; i++) {
            return n % i != 0;
        }
        return false;
    }

    public static void main(String[] args) {
        new Prime();
    }
}

Q) Write a program to print the Fibonacci series?

Ans) The famous sequence of numbers called Fibonacci series.
Each term is found by adding the two previous ones: 1+1 is 2, 1+2 is 3 ,2+3 is 5, 3+5 is 8 and so on.
The Fibonacci has applications in diverse fields from Sorting methods in Computer Science.

Code:

public class Fibonacci {

    public static void main(String[] args) {
        long limit = 429406729;
        long next = 0;// next to the last term
        long last = 1;// last term
        long sum = 0;

        while (next < limit) {
            System.out.print(last + " ");
            sum = next + last; // Add last two terms
            next = last;// Variables move forward
            last = sum; // in the series
        }
    }
}

Q) Write a program to display the Factorial of the given number

i) using recursion
ii) without recursion

Ans)

i) Using Recursion

Code:

public class Factorial2
{
    public static void main(String[] args) {
        if(args.length != 0) {
            int num = Integer.parseInt(args[0]);
            System.out.println(factorial(num));
        }
    }
    // The "factorial" static method calculates the factorial value for the
    // specified integer passed in:
    public static int factorial(int n)
    {
        if(n <= 1)
          return 1;
        else
          return n * factorial(n-1);
        // The same can be expressed using the ternary operator
        //return((n <= 1) ? 1 : (n * factorial(n-1)));
    }
}

ii) Without Recursion

Code:

public class Factorial {
    public static void main(String[] args) {
        if(args.length != 0) {
            int num = Integer.parseInt(args[0]);
            System.out.println(factorial(num));
        }
    }
    // Use a while loop
    private static int factorial(int fact) {
        int result = fact;
        if (fact == 0)
            return result;
        else {
            while (fact != 1)
                result *= --fact;
        }
        return result;
    }
    
    // Use a for loop
    private static int factorial2(int fact) {
        int result = 0;
        for (int i = fact; i > 0; i--) {
            result *= i;
        }
        return result;
    }
}

Q) Write a program to animate over a sequence of images?

Ans) Here is the same program to animate over a sequence of Images!!

You can extract images from a VCD song using VirtualDubMod software!!

VirtualDubMod Hompage

Code:

// Animating over a sequence of images!!

import java.awt.*;
import java.io.*;
import javax.imageio.ImageIO;
import javax.sound.sampled.*;
import javax.swing.*;

public class AnimApp extends JComponent implements Runnable {

    private Image image;
    private int frame = 0;
    // Total no. of Images
    private int totalImages = 97; // total no.of images
    private Clip clip;
    private static int width = 345 + 345/2;
    private static int height = 208 + 208/2;
    // Display each image
    private int delay = 135;    // 35 fps
    private String path = "resources/images";
    private String prefix = "SM";
    
    // NOTE you should create a directory called 'resources/images' in the current directory and place some images like SM1.png,
    // SM2.png, SM3.png ... SM60.png 
    

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        //Image image = images[frame];
        if (image != null) {
            // Draw the current image
            int x = 0;
            int y = 0;
            // Scale the Image to double its size
            g.drawImage(image, x, y, width, height, this);
        }
    }

    public Image getImage(int frame) {
        try {
            return ImageIO.read(new File(path + prefix + frame + ".png"));
        } catch (IOException ioe) {
        }
        return null;
    }

    public void print(String message) {
        System.out.println(message);
    }

    @Override
    public void run() {

        try {
            while (true) {
                // Fetch the Image
                image = getImage(frame);
                // Move to the next image
                frame = (frame + 1) % totalImages;
                // Causes the paint() method to be called
                repaint();
                // Wait
                Thread.sleep(delay, 200);
            }
        } catch (InterruptedException e) {
        }
    }

    public static void showFrame() {
        AnimApp app = new AnimApp();
        // Display the animation in a frame
        JFrame frame = new JFrame();
        frame.getContentPane().add(app);
        frame.setSize(width, height);
        frame.setResizable(false);
        frame.setLocationRelativeTo(app);
        frame.setVisible(true);
        frame.setTitle("Animation App");
        frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
        (new Thread(app)).start();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                AnimApp.showFrame();
            }
        });
    }
}

*s21.postimg.org/fi5gf1hxv/Animation_App.png

Q) Write a program to print the Directory report (file types , size (MB)) , Use recursion to process the sub-directories?
Also calculate the entire directory size(in GB) ?

Ans) Here is the complete code!!

Code:

/**
 * @(#)FileExtensions.java
 *
 * @author JGuru
 * @version 1.00 2015/7/30
 */
import java.io.File;
import java.util.Vector;

public class FileExtensions {

    private String path = "."; // This represents the current directory
    private File file = new File(path);
    private Vector<String> fileExtension = new Vector<>();
    private String extension = "";
    //Total size of the directory
    private long totalSize = 0;
    private int MAX;
    //Array holding file sizes
    private int[] fileSizes;

    public FileExtensions() {

        // Get all the unique file extentions
        getFileExtensions(file);
        System.out.println("\n\nDirectory Report for " + file.getAbsolutePath() + "\n\n");
        System.out.println("Directory Total Size : " + toGB(totalSize) + " GB");
        // Create an array to hold files size
        MAX = fileExtension.size();
        fileSizes = new int[MAX];
        // get all the files size
        getFilesSize(file);
        System.out.println(" File Type Size (in MB)" + "\n");
        long size;
        for (int i = 0; i < MAX; i++) {
            // Convert the size in bytes to MB!!
            size = toMB(fileSizes[i]);
            // Print fewer !!
            if (size > 10) {
                System.out.println(fileExtension.get(i) + "\t\t" + size + " MB");
            }
        }
    }

    // Process all files and directories under the directory
    public void getFileExtensions(File file) {
        if (file != null) {
            // The file is a directory
            if (file.isDirectory()) {

                String[] children = file.list();
                if (children != null) {
                    for (int i = 0; i < children.length; i++) {
                        getFileExtensions(new File(file, children[i]));
                    }
                }

            } else {
                // Accumulate the file size
                totalSize += file.length();
                extension = getExtension(file);
                if (!isDigit(extension)) {
                    if (!fileExtension.contains(extension)) {
                        fileExtension.addElement(extension);
                    }
                }
            }
        }
    }

    public String getExtension(File file) {
        if (file != null) {
            String fileName = file.getName().toLowerCase();
            int dotIndex = fileName.lastIndexOf(".");
            return fileName.substring(dotIndex + 1);
        }
        return null;
    }

    // Returns the Files size in MB
    public void getFilesSize(File file) {
        if (file != null) {
            if (file.isFile()) {
                for (int i = 0; i < MAX; i++) {
                    if (getExtension(file).equals(fileExtension.get(i))) {
                        fileSizes[i] += file.length();
                    }
                }
            }

            if (file.isDirectory()) {
                String[] children = file.list();
                if (children != null) {
                    for (int i = 0; i < children.length; i++) {
                        getFilesSize(new File(file, children[i]));
                    }
                }
            }
        }
    }

    // Converts bytes to GB
    long toGB(long bytes) {
        // 1 GB = 1074213536.686391 bytes
        //1074213536.686391 bytes - 1GB
        //bytes ?
        return (long) (bytes * 1 / (1074213536.686391));
    }

    public FileExtensions(int MAX, int[] fileSizes) {
        this.MAX = MAX;
        this.fileSizes = fileSizes;
    }

    // Converts bytes to MB
    int toMB(long bytes) {
        return (int) ((bytes * 457) / 479562693);
    }

    // Check whether the first character is a digit
    boolean isDigit(String str) {
        if (str != null) {
            char c = str.charAt(0);
            if (Character.isDigit(c)) {
                return true;
            }
        }
        return false;
    }

    void print(String str) {
        System.out.println(str);
    }

    public static void main(String args[]) {
        new FileExtensions();
    }
}

The program recursively searches a given directory for files (caches the extensions) & finds the sizes of the files with all the extensions.
The method toGB() converts the size in bytes to GB. Similarly the method toMB converts the size from bytes to MB.

Q) Write a program to find the largest word in a String?

Ans) Here is the solution!!

Code:

// Find the Largest word in a String
/**
 *
 * Author JGuru - dated 31-12-2005
 */
class LargestWord {

    String str = "Hey Java is great programming language oops!!";
    //Convert the String into a String array (easy for comparing items)
    String strArr[] = str.split("\\s");

    // Compare the String Length of two Strings
    // return the bigger length one
    private String compare(String str1, String str2) {

        if (str1.length() > str2.length()) {
            return str1;
        } else {
            return str2;
        }
        //return str1.length() > str2.length() ? str1 : str2;
    }

    LargestWord() {
        String tmp = "";
        for (int i = 0; i < strArr.length; i++) {
            //Initialize variable tmp with the element '0' in the array
            if (i == 0) {
                tmp = strArr[0];
            } else {
                // Compare both strings , store the result in tmp variable
                tmp = compare(tmp, strArr[i]);
            }
        }
        System.out.println("Largest word = " + tmp);
    }

    public static void main(String[] s) {
        new LargestWord();
    }
}

Here we want find the largest word in a String. First we split the String into a String array.
We use a method called compare() to compare two strings , return the one with bigger length.
We iterate through the array ans atlast find the bigger string.

17) Write a program to print the factorial of a number (very very big number) ?

Ans) int, long, double can't hold very very very big numbers!!!

The solution is to use java.math.BigInteger!!
BigInteger can hold very very very long numbers!! It treats numbers as Strings.

Here is the code.

Code:

import java.math.BigInteger;

// Big Numbers Factorial
public class FactorialBig {

    public static void main(String[] args) {
        if (args.length != 0) {
            int num = Integer.parseInt(args[0]);
            System.out.println(factorial(num));
        }
    }

    private static BigInteger factorial(int fact) {
        BigInteger m = new BigInteger("1");
        for (int i = fact; i > 0; i--) {
            m = m.multiply(new BigInteger("" + i));
        }
        return m;
    }
}

To run this program type :

java FactorialBig 10000

Here is the output!!

Code:

2846259680917054518906413212119868890148051401702799230794179994274411340003764443772990786757784775815884
0621423175288300423399401535187390524211613827161748198241998275924182892597878981242531205946599625986706
5601615720360323979263287367170557419759620994797203461536981198970926112775004841988454104755446424421365
7330307670362882580354896746111709736957860367019107151273058728104115864056128116538532596842582599558468
8146430425589836649317059251717204276597407446133400054194052462303436869154059404066227828248371512038322
1786446271838229238996389928272218797024593876938030946273322925705554596900278752822425443480211275590191
6942542902891690721909708369053987374745248337289952180236328274121704026808676921045155584056717255537201
5852132829034279989818449313610640381489304499621599999359670892980190336998484404665419236258424947163178
9611920412331082686510713545168455409360330096072103469443779823494307806260694223026818852275920570292308
4312618849760656074258627944882715595683153344053442544664841689458042570946167361318760523498228632645292
1529423479870603344290737158688499178932580691483168854251956006172372636323974420786924642956012306288720
1226529529640915083013366309827338063539729015065818225742954758943997651138655412081257886837042392087644
8476156900126488927159070630640966162803878404448519164379080718611237062213341541506599184387596102392671
3276546986163657706626438638029848051952769536195259240930908614471907390768585755934786981720734372093104
8254756285677776940815640749622752549933841128092896375169902198704924056175317863469397980246197370790418
6832993101655415074230839317687836692369484902599960772968429397742753626311982541668153189176323483919082
1000147178932184227805135181734921901146246875769835373441456013122615221391178759688367364087207937002992
0382791980387023720780391403123689976081528403060511167094847222248703891999934420713958369830639622320791
1562404425080891991431983712044559834404755675948921210149815245454359428541439084356441998422485547853216
3624030098442855331829253154206551237079705816393460296247697010388742206441536626733715428700789122749340
6843364428898471008406416000936239352612480379752933439287643983163903127764507224792678517008266695983895
2615075900734921519759265919270887320259406638211880198885474826604834225645770574397312225970067193606176
3513579529821794290797705327283267501488024443528681645026165662837546519006171873442260438919298506071515
3900311066847273601358167064378617567574391843764796581361005996386895523346487817461432435732248643267984
8198145843270303589550842053478849336458248259203328808902578238823326577020524897093704721021424841334246
5268206806732314214483854074182139621846870108359582946965235632764870475718351616879235068366271743711915
7233611430701211207676086978515597218464859859186436417168508996255168209107935702311185181747750108046225
8552131476489749066075287708289766751495100968232968973200062239288805665803614031128546592908407803397490
0664953205873164948093883816198658850827382468034897864757116679890423568018303504133875731972630897909435
7106877973016339180878684749436335338933735869064058484178280651962758264344292580584222129476494029486226
7076183298822900407239040373316820741741325165668844307933944701920890562078838758534251282095735930701819
7708340163817638278562539516825426644614941044711579533262372815468794080423718587423026200264221822694188
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Wow, the ouput is massive!!!

The same program using Java Swing is as follows...

Code:

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.math.BigInteger;
import javax.swing.*;

// Big Numbers Factorial
public class FactorialBig extends JFrame {

    private JTextField textField = new JTextField(23);
    private JTextArea textArea = new JTextArea();
    private JButton process = new JButton("Process");
    private Font font = new Font("Dialog", Font.BOLD, 15);
    private int number = 0;
    private String output = "";
    private String outputScientific = "";
    private JCheckBox scientific = new JCheckBox("Scientific");

    public FactorialBig() {

        // Nimbus look'n feel
        try {
            for (UIManager.LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException | IllegalAccessException | InstantiationException | UnsupportedLookAndFeelException e) {
            // Do nothing
        }
        // update the UI
        textField.updateUI();
        textArea.updateUI();
        process.updateUI();
        scientific.updateUI();

        // Set the font
        textField.setFont(font);
        textArea.setFont(font);
        textArea.setLineWrap(true);
        textArea.setEditable(false);
        JPanel top = new JPanel(new FlowLayout(FlowLayout.CENTER));
        top.add(new JLabel("Enter a Number : "));
        top.add(textField);
        top.add(scientific);
        top.add(process);
        add(top, BorderLayout.NORTH);

        scientific.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                if (scientific.isSelected()) {
                    textArea.setText(outputScientific);
                } else {
                    textArea.setText(output);
                }
            }
        });

        process.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent ae) {
                textArea.setText("");

                String input = textField.getText();
                // The user has not entered anything
                if (input.equals("")) {
                    JOptionPane.showMessageDialog(null, "Sorry no input!!");
                } else {
                    new Thread(new Runnable() {

                        @Override
                        public void run() {
                            setCursor(new Cursor(Cursor.WAIT_CURSOR));
                            process.setEnabled(false);
                            try {
                                number = Integer.parseInt(textField.getText());
                                output = "" + factorial(number);
                                outputScientific = toScientific(output);
                                if (scientific.isSelected()) {
                                    textArea.setText(outputScientific);
                                } else {
                                    textArea.setText(output);
                                }

                            } catch (NumberFormatException nfe) {
                                JOptionPane.showMessageDialog(null, "OOps not a valid number !!!");
                                textField.setText("");
                                textArea.setText("");
                                process.setEnabled(true);
                                setCursor(new Cursor(Cursor.DEFAULT_CURSOR));
                            }
                            process.setEnabled(true);
                            //Scroll to the bottom of the textArea
                            textArea.setCaretPosition(textArea.getDocument().getLength());
                            setCursor(new Cursor(Cursor.DEFAULT_CURSOR));
                        }
                    }).start();
                }
            }
        });

        add(new JScrollPane(textArea), BorderLayout.CENTER);

        setSize(800, 600);
        setTitle("FactorialDemo");
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    private String toScientific(String str) {
        if (str.length() > 12) {
            String firstDigit = str.substring(0, 1);
            String restDigit = str.substring(1, 30);
            return firstDigit + "." + restDigit + "e+" + (str.length() - 1);
        }
        return str;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new FactorialBig();
            }
        });
    }

    private BigInteger factorial(int fact) {
        BigInteger m = new BigInteger("1");
        for (int i = 1; i <= fact; i++) {
            m = m.multiply(new BigInteger("" + i));
        }
        return m;
    }
}

*s12.postimg.org/l6mf0zwe1/Factorial_Big.png

Enter a number & press the 'Process' button. If you want the scientific notation select the scientific checkbox.

Q) Write a program to zoom a given image to 25%, 50%, 100%, 150%, 200% and so on ?

Code:

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

/**
 * Created with IntelliJ IDEA.
 * User: Sowndar
 * Date: 7/20/14
 * Time: 1:20 PM
 * To change this template use File | Settings | File Templates.
 */
public class ImageZoomCombo extends JFrame {

    private final String []zFactor = new String[] {"10%", "25%", "50%", "75%", "100%", "125%", "150%", "200%", "250%", "300%", "450%", "500%", "600%", "700%", "800%"};
    private final JComboBox <String> comboBox = new JComboBox<>(zFactor);
    private Image image;
    private final JLabel label = new JLabel();
    private int imgWidth, imgHeight;

    public ImageZoomCombo() {
        //Set System look'n feel
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException e) {
            System.err.println("Error loading look 'n feel!!");
        }
        comboBox.updateUI();
        // Alignment for the Label
        label.setHorizontalAlignment(SwingConstants.CENTER);
        label.setVerticalAlignment(SwingConstants.CENTER);
        comboBox.setPreferredSize(new Dimension(150, 30));
        comboBox.setSelectedItem("100%");
        comboBox.addItemListener(new ItemListener() {
            @Override
            public void itemStateChanged(ItemEvent e) {
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        // Catch the OutOfMemoryError error, in case it happens!!
                        try
                        {
                            String zoomFactor = comboBox.getSelectedItem().toString();
                            //Remove the percent (%) sign from the String
                            zoomFactor = zoomFactor.substring(0, zoomFactor.lastIndexOf("%"));
                            int zoomValue = 100;
                            try
                            {
                                zoomValue = Integer.parseInt(zoomFactor);
                            }  catch (NumberFormatException nfe) {
                                zoomValue = 100;
                            }
                            setCursor(new Cursor(Cursor.WAIT_CURSOR));
                            label.setIcon(new ImageIcon(image.getScaledInstance(imgWidth * zoomValue/100, imgHeight * zoomValue/100, Image.SCALE_SMOOTH)));
                            setCursor(new Cursor(Cursor.DEFAULT_CURSOR));
                        }  catch (OutOfMemoryError ome) {
                            JOptionPane.showMessageDialog(null, "Oops, The JVM is running out of Memory (Heap)!! \n Start the JVM with -Xms128m -Xmx256m argument", "Error", JOptionPane.ERROR_MESSAGE);
                            System.exit(-1);
                        }
                    }
                }).start();
            }
        });

        //Get the Image
        image = getImage("Images/Andrea Mantea3.jpg");
        if(image != null) {
            imgWidth = image.getWidth(this);
            imgHeight = image.getHeight(this);
            label.setIcon(new ImageIcon(image));
        }
        add(new JScrollPane(label));
        JPanel top = new JPanel(new FlowLayout(FlowLayout.CENTER));
        top.add(new JLabel("ImageZoom Combo"));
        top.add(comboBox);
        add(top, BorderLayout.NORTH);
        Dimension scrDim = Toolkit.getDefaultToolkit().getScreenSize();
        setSize(scrDim.width/2 + 120, scrDim.height);
        setTitle("ImageZoom");
        setVisible(true);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }

    public BufferedImage getImage(String fileName) {
        try {
            return ImageIO.read(new File(fileName));
        } catch (IOException ioe) {
            System.err.println("Error loading Image : " + fileName + "!!");
            System.exit(-1);
        }
        return null;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new ImageZoomCombo();
            }
        });
    }
}

*s16.postimg.org/coxbdf1xt/Image_Zoom_Combo.png

Q) Write a program to show a simple calculator in action ?

Code:

//JavaCalculator.java

/**
 * Created with IntelliJ IDEA.
 * User: Sowndar
 * Date: 11/15/14
 * Time: 1:59 PM
 * To change this template use File | Settings | File Templates.
 */
// A Simple Calculator

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class JavaCalculator extends JFrame {

    private JLabel label;
    private boolean firstDigit = true;
    private float savedValue = 0.0f; // Initial value
    private String operator = "="; // Initial operator
    private Font font = new Font("Serif", Font.BOLD, 16);

    public JavaCalculator() {
        try
        {
           UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception e) {

        }
        label = new JLabel("0", JLabel.RIGHT);
        label.setFont(font);
        label.setBackground(Color.white);
        add("North", label);
        JPanel panel = new JPanel();
        panel.setLayout(new GridLayout(4, 4));
        addButtons(panel, "789/");
        addButtons(panel, "456*");
        addButtons(panel, "123-");
        addButtons(panel, ".0=+");
        add("Center", panel);
        setSize(250, 200);
        setTitle("Java Calculator");
        setLocationRelativeTo(null);
        setVisible(true);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }

    public void addButtons(JPanel panel, String labels) {
        int MAX = labels.length();
        JButton []button = new JButton[MAX];
        String text = "";
        for (int i = 0; i < MAX; i++) {
            text = labels.substring(i, i + 1);
            button[i] = new JButton(text);
            button[i].setActionCommand(text);
            button[i].setFont(font);
            button[i].addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent ae) {

                    String s = ae.getActionCommand();
                    if ("0123456789.".indexOf(s) != -1) { // isDigit
                        if (firstDigit) {
                            firstDigit = false;
                            label.setText(s);
                        } else {
                            label.setText(label.getText() + s);
                        }
                    } else { // isOperator
                        if (!firstDigit) {
                            compute(label.getText());
                            firstDigit = true;
                        }
                        operator = s;
                    }
                }
            });
            panel.add(button[i]);
        }
    }

    public void compute(String s) {
        float sValue = new Float(s).floatValue();
        char c = operator.charAt(0);
        if(c == '=') {
            savedValue = sValue;
        }
        else if(c == '+') {
            savedValue += sValue;
        }
        else if(c == '-') {
            savedValue -= sValue;
        }
        else if(c == '*') {
            savedValue *= sValue;
        }
        else if(c == '/') {
            savedValue /= sValue;
        }
        label.setText(String.valueOf(savedValue));
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new JavaCalculator();
            }
        });
    }
}

*s11.postimg.org/io6x3dqjj/Java_Calculator.png

5) Write a program to list the contents of a directory as Icons (Simillar to Windows's View As Icons) ?

Ans) Here is the solution code!!

Code:

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.File;
import javax.swing.UIManager.*;
import javax.swing.border.MatteBorder;
import javax.swing.filechooser.FileSystemView;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.util.*;

/**
 * Created with IntelliJ IDEA.
 * User: Sowndar Date: 6/1/15 Time: 3:03 PM To
 * change this template use File | Settings | File Templates.
 */
public class ViewAsIcons extends JFrame {

    private int MAX;
    private JButton[] button;
    private Desktop desktop = Desktop.getDesktop();
    private ImageIcon icon;
    private Image iconImage;
    private MatteBorder matte = new MatteBorder(3, 3, 3, 3, Color.black);
    private ImageIcon dirIcon = null;

    public ViewAsIcons(String dirName) {
        // set the System look 'n feel
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException | IllegalAccessException | InstantiationException | UnsupportedLookAndFeelException e) {
            // Do nothing
        }
        setLayout(new BorderLayout());
        JPanel panel = new JPanel();
        int cols = 4;
        int rows = MAX / cols;
        panel.setLayout(new GridLayout(rows, cols, 5, 5));
        File directory = new File(dirName);
        if (directory.exists()) {
            //Get the directory contents
            String[] dirList = directory.list();
            File file = null;
            MAX = dirList.length;
            if (MAX > 0) {
                button = new JButton[MAX];
                // Show the directories first, then the files
                Vector <String>fileVector = new Vector<>();
                Vector <String>dirVector = new Vector<>();

                for (int i = 0; i < MAX; i++) {
                    file = new File(dirName + System.getProperty("file.separator") + dirList[i]);
                    if(file.isDirectory()) {
                        dirVector.addElement(file.getName());
                    }
                    else
                    {
                        fileVector.addElement(file.getName());
                    }
                }

                String []tmp = new String[dirVector.size()];
                dirVector.copyInto(tmp);

                String []tmp2 = new String[fileVector.size()];
                fileVector.copyInto(tmp2);

                Vector <String>tmpVector = new Vector<>();
                for (int i = 0; i < tmp.length; i++) {
                    tmpVector.addElement(tmp[i]);
                }
                for (int i = 0; i < tmp2.length; i++) {
                    tmpVector.addElement(tmp2[i]);
                }

                dirList = new String[tmpVector.size()];
                for (int i = 0; i < tmpVector.size(); i++) {
                    dirList[i] = tmpVector.get(i);
                }

                String extension = "";
                for (int i = 0; i < MAX; i++) {
                    file = new File(dirName + System.getProperty("file.separator") + dirList[i]);
                    button[i] = new JButton(dirList[i]);
                    button[i].setVerticalTextPosition(SwingConstants.BOTTOM);
                    button[i].setHorizontalTextPosition(SwingConstants.CENTER);
                    button[i].setActionCommand(file.toString());

                    button[i].addActionListener(new ActionListener() {

                        @Override
                        public void actionPerformed(ActionEvent ae) {
                            Object source = ae.getSource();
                            for (int j = 0; j < button.length; j++) {
                                button[j].setBorder(null);
                                if(button[j] == source) {
                                    button[j].setBorder(matte);
                                }
                            }
                            try {
                                desktop.open(new File(ae.getActionCommand()));
                            } catch (IOException e) {

                            }
                        }
                    });
                    if (file.isDirectory()) {

                        if(dirIcon == null) {
                            icon = (ImageIcon)FileSystemView.getFileSystemView().getSystemIcon(file);
                            iconImage = icon.getImage();
                            // Scale the Image to thrice its size
                            iconImage = iconImage.getScaledInstance(iconImage.getWidth(null)*3, iconImage.getHeight(null)*3, Image.SCALE_SMOOTH);
                            dirIcon = new ImageIcon(iconImage);
                            button[i].setIcon(dirIcon);
                        }
                        else
                        {
                            button[i].setIcon(dirIcon);
                        }
                        button[i].setToolTipText("Directory");

                    } else {
                        // It's a File
                        extension = file.getName();
                        extension = extension.substring(extension.lastIndexOf(".")+1);
                        button[i].setToolTipText(extension.toUpperCase() + " File");
                        icon = (ImageIcon)FileSystemView.getFileSystemView().getSystemIcon(file);
                        iconImage = icon.getImage();
                        // Scale the Image to twice its size
                        iconImage = iconImage.getScaledInstance(iconImage.getWidth(null)*2, iconImage.getHeight(null)*2, Image.SCALE_SMOOTH);

                        button[i].setIcon(new ImageIcon(iconImage));
                    }

                    button[i].setPreferredSize(new Dimension(150, 90));
                    panel.add(button[i]);
                }
                add(new JScrollPane(panel));
                setSize(800, 600);
                setTitle("ViewAsIcons");
                setVisible(true);
                setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
            } else {
                System.out.println("Sorry, No files found!!");
            }
        } else {
            System.out.println("Sorry, the specified directory doesn't exists!!!");
        }
    }

    public static void main(final String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new ViewAsIcons(args[0]);
            }
        });
    }
}

*s11.postimg.org/bojv55wv3/View_As_Icons.png

Here we get the contents of the specified directory using the list() method. We create an array of buttons then finally we add them to a scrollpane.

6) Write a program to list the contents of a directory in a table format?

Ans)

Code:

import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableModel;
import java.io.File;
import java.util.Date;

/**
 * Created with IntelliJ IDEA.
 * User: Sowndar
 * Date: 6/1/15
 * Time: 4:13 PM
 * To change this template use File | Settings | File Templates.
 */
public class ViewAsTable extends JFrame {

    private int MAX;
    private String[] columns = {"Name",
            "Date Modified",
            "Type",
            "Size"};
    private Object rows[][];
    private String []readFormat = ImageIO.getReaderFormatNames();

    public ViewAsTable(String dirName) {


        try {
            for (UIManager.LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (Exception e) {
            // If Nimbus is not available, you can set the GUI to another look and feel.
        }
        File directory = new File(dirName);
        if(directory.exists()) {
            String []dirList = directory.list();
            MAX = dirList.length;
            if(MAX > 0) {
                rows = new Object[MAX][4];
                File file = null;
                int fileSize = 0;
                String fileName = "";
                for (int row = 0; row < MAX ; row++) {
                    for (int col = 0; col < 3; col++) {
                        file = new File(dirName + System.getProperty("file.separator") + dirList[row]);
                        rows[row][0] = file.getName();
                        rows[row][1] = new Date(file.lastModified());
                        if(file.isDirectory()) {
                            rows[row][2] = " Directory";
                        }
                        else
                        {
                            if(dirList[row].endsWith("bat")) {
                                fileName = "BATCH File";
                            }
                            else if(dirList[row].endsWith("dll")){
                                fileName = "DLL File";
                            }
                            else if(isImage(dirList[row])){
                                fileName = "Image File";
                            }
                            else if(dirList[row].endsWith("html") || dirList[row].endsWith("htm")) {
                                 fileName = "HTML File";
                            }
                            else if(dirList[row].endsWith("jar")){
                                 fileName = "JAR File";
                            }
                            else if(dirList[row].endsWith("java")) {
                                 fileName = "JAVA File";
                            }
                            else if(dirList[row].endsWith("pdf")) {
                                fileName = "PDF File";
                            }
                            else if(dirList[row].endsWith("mpg") || dirList[row].endsWith("mov") || dirList[row].endsWith("wmv")) {
                                fileName = "Video File";
                            }
                            else if(dirList[row].endsWith("xml")) {
                                fileName = "XML File";
                            }
                            else if(dirList[row].endsWith("zip")) {
                                fileName = "ZIP File";
                            }
                            else if(dirList[row].endsWith("exe")) {
                                fileName = "EXE File";
                            }
                            else if(dirList[row].endsWith("class")) {
                                fileName = "CLASS File";
                            }
                            else {
                                fileName = "File";
                            }

                                rows[row][2] = fileName;
                        }
                        fileSize =  new Integer((int) getSizeInKB(file.length()));
                        if(fileSize < 1) {
                            fileSize = 1;
                        }
                        rows[row][3] = fileSize;
                    }
                }
                TableModel model = new DefaultTableModel(rows, columns) {

                    @Override
                    public Class getColumnClass(int column) {
                        Class returnValue = null;
                        try {
                            if ((column >= 0) && (column < getColumnCount())) {
                                returnValue = getValueAt(0, column).getClass();
                            } else {
                                returnValue = Object.class;
                            }
                            return returnValue;
                        } catch (Exception e) {
                        }
                        return null;
                    }
                };

                add(new JScrollPane(new JTable(model)));
                setSize(800, 600);
                setTitle("ViewAsTable");
                setVisible(true);
                setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
            }
            else
                System.out.println("Sorry, No files found!!");
        }
        else
        {
            System.out.println("The specified directory doesn't exist!!!");
            System.exit(-1);
        }

    }

    public boolean isImage(String fileName) {
        for (int i = 0; i < readFormat.length ; i++) {
            if(fileName.endsWith(readFormat[i]))
                return  true;
        }
        return false;
    }

    public double getSizeInKB(long size) {
        //98.3 KB (1,00,756 bytes)
        // 1,00,756 bytes -> 98.3 KB
        // size ? (size*98.3)/100756;
        return (size * 98.3) / 100756;
    }

    public static void main(final String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new ViewAsTable(args[0]);
            }
        });
    }
}

*s12.postimg.org/sozoeoefd/View_As_Table.png

Here we get the contents of the specified directory & convert the array of String to table format. finally add the table to a scrollpane.

15) Write a program to filter out the images in the 'Images' directory & display them as a List (using JList)?
Also selecting an List item should display the corresponding Image. You need to create a directory called 'Images'
under the current directory for this program to run.

Ans)

Code:

import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.io.File;
import java.io.FilenameFilter;
import java.io.IOException;
import java.lang.String;
import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.ImageIcon;

/**
 * Created with IntelliJ IDEA. User Sowndar Date: 8/1/14 Time: 2:28 PM To change
 * this template use File | Settings | File Templates.
 */
public class ListDemo extends JFrame {

    private String path = "Images/";
    private String[] imgName;
    private JList<String> list = new JList<>();
    private int MAX;
    private JLabel label = new JLabel();
    private ImageIcon icon = new ImageIcon("Icons/image_32x32.png");
    private Dimension scrDim;
    private int width, height;

    //NOTE : You need to create a directory called 'Images' in the current directory and place some JPG or PNG images there
    // atleast 10 or 15 will do!!
    public ListDemo() {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException | IllegalAccessException | InstantiationException | UnsupportedLookAndFeelException e) {
            // Do nothing
        }
        scrDim = Toolkit.getDefaultToolkit().getScreenSize();
        width = scrDim.width;
        height = scrDim.height;

        list.updateUI();
        File directory = new File(path);
        if (!directory.exists()) {
            System.err.println("The specified directory doesn't exist!!");
            System.exit(-1);
        }
        // Filter out the Images
        imgName = directory.list(new FilenameFilter() {


            @Override
            public boolean accept(File dir, String name) {
                return name.endsWith("jpg");
            }
        });
        for (int i = 0; i < imgName.length; i++) {
		     // Discard the file extension
		     imgName[i] = imgName[i].substring(0, imgName[i].lastIndexOf("."));
        }
        MAX = imgName.length;

        if (MAX == 0) {
            System.err.println("OOps , No Images found!!");
            System.exit(-1);
        }
        //set the List data items
        list.setListData(imgName);
        //Select more than 1 item use the SHIFT key (hold it)!!
        list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        list.setCellRenderer(new ImageRenderer());

        final JSplitPane splitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, new JScrollPane(list), label);
        splitPane.setDividerLocation(350);
        splitPane.setOneTouchExpandable(true);
        // Listen for Mouse events
        list.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                String selected = list.getSelectedValue();
                label.setIcon(new ImageIcon(getImage(path + selected + ".jpg")));
            }
        });

        add(splitPane);
        setTitle("ListDemo");
        setSize(width, height);
        setVisible(true);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }

    //Get the Image
    public Image getImage(String fileName) {
            try {
                return ImageIO.read(new File(fileName));
            } catch (IOException ioe) {
                System.err.println("Error loading Image : " + fileName);
            }

        return null;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new ListDemo();
            }
        });
    }

    //  Inner class  for rendering icon for the List
    class ImageRenderer extends JLabel implements ListCellRenderer<Object> {

        Dimension dim = new Dimension(210, 74);

        ImageRenderer() {
            setOpaque(true);
        }

        @Override
        public Component getListCellRendererComponent(JList<?> list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
            //  If this is the selection value request from a combo box
            //  then find out the current selected index from the list.
            if (index == -1) {
                int selected = list.getSelectedIndex();
                if (selected == -1) {
                    return this;
                } else {
                    index = selected;
                }
            }
            setText(value.toString());
            try {
                if (icon != null) {
                    setIcon(icon);
                }

            } catch (Exception e) {
            }
            setPreferredSize(dim);
            setFont(list.getFont());
            if (isSelected) {
                setBackground(list.getSelectionBackground());
                setForeground(list.getSelectionForeground());
            } else {
                setBackground(list.getBackground());
                setForeground(list.getForeground());
            }
            return this;
        }
    }
}

*s4.postimg.org/i0kyj3s4p/List_Demo.png

The program filters the images in the 'Images' directory. We create a List using the found values. Clicking on a list item displays the corresponding image.

16) Write a program to filter the images in the 'Images' directory & display them using a JComboBox. Also create next & previous
button, to display the next & previous image.You need to create a directory called 'Images'
under the current directory for this program to run.

Ans)

Code:

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.io.File;
import java.io.FilenameFilter;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.*;

/**
 * Created with IntelliJ IDEA. User Sowndar Date: 8/1/14 Time: 2:28 PM To change
 * this template use File | Settings | File Templates.
 */
public class ComboBoxDemo extends JFrame implements ActionListener {

    private String path = "Images/";
    private String[] imgName;
    private JComboBox<String> comboBox;
    private int MAX;
    private JLabel label = new JLabel();
    private ImageIcon icon = new ImageIcon("Icons/image_32x32.png");
    private JButton back;
    private JButton forward;
    private int index = 0;

    public ComboBoxDemo() {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException | IllegalAccessException | InstantiationException | UnsupportedLookAndFeelException e) {
            // Do nothing
        }

        label.setHorizontalAlignment(SwingConstants.CENTER);
        label.setVerticalAlignment(SwingConstants.CENTER);
        File directory = new File(path);
        if (!directory.exists()) {
            System.err.println("The specified directory doesn't exist!!");
            System.exit(-1);
        }
        // Filter out the Images
        imgName = directory.list(new FilenameFilter() {
            String[] readFormat = ImageIO.getReaderFormatNames();

            @Override
            public boolean accept(File dir, String name) {
                for (int i = 0; i < readFormat.length; i++) {
                    if (name.endsWith(readFormat[i])) {
                        return true;
                    }
                }
                return false;
            }
        });
        back = new JButton(new ImageIcon("resources/back.png"));
        forward = new JButton(new ImageIcon("resources/forward.png"));
        back.setToolTipText("Previous");
        back.setBorderPainted(false);
        back.setContentAreaFilled(false);
        forward.setToolTipText("Next");
        forward.setBorderPainted(false);
        forward.setContentAreaFilled(false);
        // Add the listeners to the buttons
        back.addActionListener(this);
        forward.addActionListener(this);

        MAX = imgName.length;

        if (MAX == 0) {
            System.err.println("OOps , No Images found!!");
            System.exit(-1);
        }
        comboBox = new JComboBox<>(imgName);
        JPanel top = new JPanel(new FlowLayout(FlowLayout.CENTER));
        top.add(new JLabel("Select a Image: "));
        top.add(comboBox);
        add(top, BorderLayout.NORTH);
        add(new JScrollPane(label), BorderLayout.CENTER);
        comboBox.setRenderer(new ImageRenderer());
        comboBox.addItemListener(new ItemListener() {

            @Override
            public void itemStateChanged(ItemEvent e) {
                String selected = comboBox.getSelectedItem().toString();
                label.setIcon(new ImageIcon(path + "/" + selected));
            }
        });
        JPanel bottom = new JPanel(new FlowLayout(FlowLayout.CENTER, 150, 5));
        bottom.add(back);
        bottom.add(forward);
        add(bottom, BorderLayout.SOUTH);
        //Show the first Image
        label.setIcon(new ImageIcon(path + "/" + imgName[0]));
        setTitle("ComboBoxDemo");
        Dimension scrDim = Toolkit.getDefaultToolkit().getScreenSize();
        setSize(scrDim.width / 2 + 150, scrDim.height);
        setVisible(true);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }

    @Override
    public void actionPerformed(ActionEvent ae) {
        Object source = ae.getSource();
        if (source == back) {
            index = comboBox.getSelectedIndex();
            if (index <= 0) {
                index = imgName.length;
            }
            index--;
            comboBox.setSelectedIndex(index);
        } else if (source == forward) {
            index = comboBox.getSelectedIndex();
            index++;
            if (index >= imgName.length) {
                index = 0;
            }
            comboBox.setSelectedIndex(index);
        }
    }

    //Get the Image
    public Image getImage(String fileName) {
        try {
            return ImageIO.read(new File(fileName));
        } catch (IOException ioe) {
            System.err.println("Error loading Image : " + fileName);
        }
        return null;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new ComboBoxDemo();
            }
        });
    }

    //  Inner class  for Image preview for the comboBox
    class ImageRenderer extends JLabel implements ListCellRenderer<Object> {

        Dimension dim = new Dimension(210, 74);

        ImageRenderer() {
            setOpaque(true);
        }

        @Override
        public Component getListCellRendererComponent(JList<?> list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
            //  If this is the selection value request from a combo box
            //  then find out the current selected index from the list.
            if (index == -1) {
                int selected = list.getSelectedIndex();
                if (selected == -1) {
                    return this;
                } else {
                    index = selected;
                }
            }
            setText(value.toString());
            try {
                if (icon != null) {
                    setIcon(icon);
                }

            } catch (Exception e) {
            }
            setPreferredSize(dim);
            setFont(list.getFont());
            if (isSelected) {
                setBackground(list.getSelectionBackground());
                setForeground(list.getSelectionForeground());
            } else {
                setBackground(list.getBackground());
                setForeground(list.getForeground());
            }
            return this;
        }
    }
}

*s16.postimg.org/w21y1g3td/Combo_Box_Demo.png

Here we filter the images in the 'Images' directory create a ComboBox using these values. Selecting a particular item in the combobox displays the particular image.
The back & forward buttons displays the previous image & the next image in the array.

Q) Write a program display Polygons with red color and another one with blue & red patterns?

Code:

/**
 *
 * @author Sowndar
 */
import java.awt.*;
import javax.swing.*;

class PolygonDemo extends JComponent {

    private Polygon p;
    private Polygon pBase;
    private int step = 10;

    public PolygonDemo() {
        pBase = new Polygon();
        pBase.addPoint(0, 0);
        pBase.addPoint(10, 0);
        pBase.addPoint(5, 15);
        pBase.addPoint(10, 20);
        pBase.addPoint(5, 20);
        pBase.addPoint(0, 10);
        pBase.addPoint(0, 0);
        Dimension scrDim = Toolkit.getDefaultToolkit().getScreenSize();
        setPreferredSize(new Dimension(scrDim.width / 2, scrDim.height));
    }

    void scalePolygon(float w, float h) {
        p = new Polygon();
        for (int i = 0; i < pBase.npoints; ++i) {
            p.addPoint((int) (pBase.xpoints[i] * w),
                    (int) (pBase.ypoints[i] * h));
        }

    }

    void draw(Graphics2D g, int x, int y, int w, int h) {
        Graphics ng = g.create();
        try {
            ng.translate(x, y);
            scalePolygon(((float) w / 10f), ((float) h / 20f));
            ng.drawPolygon(p);
        } finally {
            ng.dispose();
        }
    }

    void fill(Graphics2D g, int x, int y, int w, int h) {
        Graphics ng = g.create();
        try {
            ng.translate(x, y);
            scalePolygon(((float) w / 10f), ((float) h / 20f));
            ng.fillPolygon(p);
        } finally {
            ng.dispose();
        }
    }

    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        // Set RenderingHints properties
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
        g2d.setRenderingHint(RenderingHints.KEY_COLOR_RENDERING, RenderingHints.VALUE_COLOR_RENDER_QUALITY);
        g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BICUBIC);

        Rectangle bounds = getBounds();

        int cx, cy, cw, ch;

        Color color;

        for (color = Color.red, cx = bounds.x, cy = bounds.y, cw = bounds.width / 2, ch = bounds.height;
                cw > 0 && ch > 0;
                cx += step, cy += step, cw -= (step * 2), ch -= (step * 2), color = darker(color, 0.9)) {
            g2d.setColor(color);
            draw(g2d, cx, cy, cw, ch);
        }

        for (cx = bounds.x + bounds.width / 2, cy = bounds.y, cw = bounds.width / 2, ch = bounds.height;
                cw > 0 && ch > 0;
                cx += step, cy += step, cw -= (step * 2), ch -= (step * 2)) {
            if (g2d.getColor() == Color.red) {
                g2d.setColor(Color.blue);
            } else {
                g2d.setColor(Color.red);
            }

            fill(g2d, cx, cy, cw, ch);
        }
    }

    static Color brighter(Color c, double factor) {
        return new Color(Math.min((int) (c.getRed() * (1 / factor)), 255),
                Math.min((int) (c.getGreen() * (1 / factor)), 255),
                Math.min((int) (c.getBlue() * (1 / factor)), 255));
    }

    static Color darker(Color c, double factor) {
        return new Color(Math.max((int) (c.getRed() * factor), 0),
                Math.max((int) (c.getGreen() * factor), 0),
                Math.max((int) (c.getBlue() * factor), 0));
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame f = new JFrame("PolygonDemo");
                f.add(new PolygonDemo());
                f.setSize(Toolkit.getDefaultToolkit().getScreenSize());
                f.setVisible(true);
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            }
        });
    }
}

*s13.postimg.org/6q569k83n/Polygon_Demo.png

This wraps up Java programming foundation!!
I hope that you liked it!! As you write more programs, solve more problems, you will be able
to master the Java programming language. Happy programming!!

Here are some books for Java programming at the introductory level.

Introductory Books for Java programming

1) Head First Java - Introductory book for Java programming

2) Thinking in Java by Bruce Eckel - Understand the core concepts of Java programming

3) Data-Structures & Algorithms in Java by Robert Lafore - Understand algorithms & data-structures

4) Beginning Java Objects (Wrox) - Understand OOPS methodology

5) Object-Oriented Programming in Java by Balagurusamy

6) Big Java Late Objects by Cay S. Horstmann (Discusses OOPS methodology)

7) Java How To Program by H M Deitel & P J Deitel (Contains many exercises, learn programming from a Java champion)

8) Object-Oriented Programming in Java by Stephen Gilbert and Bill McCarty

9) Algorithms in Java 4th edition by Robert SedgeWick (Understand algorithms & data-structures)

10) Core Java - Vol - I & II by Horstmann C S (Understand the core Java topics)

tekiagadi · Nov 18, 2016

The Good Information about Java Programming.

Foundation of Java Programming

JGuru

Wise Old Owl

tekiagadi

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