How do I create a JSlider with custom labels?

By I Wayan Saryada in Swing 0 Comment

The JSlider‘s setLabelTable() method allows you to define a custom labels for the JSlider. The label table is a Hashtable that contains an Integer number as the keys and a JLabel component as their values. The integer keys correspond to the JSlider tick where the labels will be customized.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;
import java.util.Hashtable;

public class JSliderCustomLabel extends JPanel {
    public JSliderCustomLabel() {
        initializeUI();
    }

    public static void showFrame() {
        JPanel panel = new JSliderCustomLabel();

        JFrame frame = new JFrame("JSlider Custom Label");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(JSliderCustomLabel::showFrame);
    }

    private void initializeUI() {
        setLayout(new BorderLayout());
        setPreferredSize(new Dimension(500, 200));

        JSlider slider = new JSlider(JSlider.VERTICAL, 0, 40, 0);
        slider.setMinorTickSpacing(1);
        slider.setMajorTickSpacing(5);
        slider.setPaintTicks(true);

        Hashtable<Integer, JLabel> labels = new Hashtable<>();
        labels.put(0, new JLabel("Freezing"));
        labels.put(15, new JLabel("Cold"));
        labels.put(25, new JLabel("Warm"));
        labels.put(35, new JLabel("Hot"));
        slider.setLabelTable(labels);

        slider.setPaintLabels(true);

        add(slider, BorderLayout.CENTER);
    }
}

The screen capture of the example above is:

JSlider with Custom Labels Demo

How do I create a JSlider that snap to the closest tick mark?

By I Wayan Saryada in Swing 0 Comment

The JSlider‘s setSnapToTicks() method call is used to move JSlider‘s knob to the nearest tick mark from where you positioned the knob. The default value of this property is false. To make it snap to the closest tick set this property to true.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;

public class SnapToTickJSlider extends JPanel {
    public SnapToTickJSlider() {
        initializeUI();
    }

    public static void showFrame() {
        JPanel panel = new SnapToTickJSlider();

        JFrame frame = new JFrame("JSlider - Snap to Tick");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(SnapToTickJSlider::showFrame);
    }

    private void initializeUI() {
        setLayout(new BorderLayout());
        setPreferredSize(new Dimension(500, 200));

        JSlider slider = new JSlider(JSlider.HORIZONTAL, 0, 30, 0);
        slider.setMinorTickSpacing(5);
        slider.setMajorTickSpacing(10);
        slider.setPaintLabels(true);
        slider.setPaintTicks(true);

        // Snaps to the closest tick mark next to where the user
        // positioned the knob.
        slider.setSnapToTicks(true);

        add(slider, BorderLayout.CENTER);
    }
}

The screen capture of the result of the code snippet above is:

JSlider Snap to Ticks Demo

How do I create custom exception class?

By I Wayan Saryada in Basic, Core API 0 Comment

You can define your own exception class for your application specific purposes. The exception class is created by extending the java.lang.Exception class for checked exception or java.lang.RuntimeException for unchecked exception. By creating your own Exception classes, you could identify the problem more precisely.

package org.kodejava.basic;

public class CustomExceptionExample {
    public static void main(String[] args) {
        int x = 1, y = 0;

        try {
            int z = CustomExceptionExample.divide(x, y);
            System.out.println("z = " + z);
        } catch (DivideByZeroException e) {
            e.printStackTrace();
        }
    }

    public static int divide(int x, int y) throws DivideByZeroException {
        try {
            return (x / y);
        } catch (ArithmeticException e) {
            String m = x + " / " + y + ", trying to divide by zero";
            throw new DivideByZeroException(m, e);
        }
    }
}

package org.kodejava.basic;

class DivideByZeroException extends Exception {
    DivideByZeroException() {
        super();
    }

    DivideByZeroException(String message) {
        super(message);
    }

    DivideByZeroException(String message, Throwable cause) {
        super(message, cause);
    }
}

How do I use checked and unchecked exception?

By I Wayan Saryada in Basic, Core API 0 Comment

By throwing a checked exception, you force the caller to handle the exception in a catch block. If a method throws a checked exception, it must declare that it throw the exception in the method declaration.

All exceptions are checked exceptions, except for those indicated by java.lang.Error, java.lang.RuntimeException, and their subclasses.

Runtime exception are exceptional conditions that are internal to the application, and that the application usually cannot anticipate or recover from. Runtime exceptions are those indicated by java.lang.RuntimeException and its subclasses.

RuntimeException are known as unchecked exception. It doesn’t require to declare the unchecked exception in the method declaration.

package org.kodejava.basic;

import java.io.File;
import java.io.IOException;

public class ExceptionExample {
    public static void main(String[] args) {
        // You must catch the checked exception otherwise you get a
        // compile time error.
        try {
            ExceptionExample.checkFileSize("data.txt");
        } catch (IOException e) {
            e.printStackTrace();
        }

        // The unchecked exception doesn't requires you to catch
        // it and it doesn't produce a compile time error.
        ExceptionExample.divide();
    }

    /**
     * This method throws a Checked Exception, so it must declare the
     * Exception in its method declaration
     *
     * @param fileName given file name
     * @throws IOException when the file size is to large.
     */

    public static void checkFileSize(String fileName) throws IOException {
        File file = new File(fileName);
        if (file.length() > Integer.MAX_VALUE) {
            throw new IOException("File is too large.");
        }
    }

    /**
     * This method throws a RuntimeException.
     * There is no need to declare the Exception in method declaration
     *
     * @return a division result.
     * @throws ArithmeticException when arithmetic exception occurs.
     */
    public static int divide() throws ArithmeticException {
        int x = 1, y = 0;
        return x / y;
    }
}

How do I convert raw IP address to String?

By I Wayan Saryada in Core API, Networking 0 Comment

This example show you how to convert a raw IP address, an array of byte, returned by InetAddress.getAddress() method call to its string representation.

package org.kodejava.net;

import java.net.InetAddress;
import java.net.UnknownHostException;

public class RawIPToString {
    public static void main(String[] args) {
        byte[] ip = new byte[0];
        try {
            InetAddress address = InetAddress.getLocalHost();
            ip = address.getAddress();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
        String ipAddress = RawIPToString.getIpAddress(ip);
        System.out.println("IP Address = " + ipAddress);

        try {
            InetAddress address = InetAddress.getByName("google.com");
            ip = address.getAddress();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
        ipAddress = RawIPToString.getIpAddress(ip);
        System.out.println("IP Address = " + ipAddress);
    }

    /**
     * Convert raw IP address to string.
     *
     * @param rawBytes raw IP address.
     * @return a string representation of the raw ip address.
     */
    private static String getIpAddress(byte[] rawBytes) {
        int i = 4;
        StringBuilder ipAddress = new StringBuilder();
        for (byte raw : rawBytes) {
            ipAddress.append(raw & 0xFF);
            if (--i > 0) {
                ipAddress.append(".");
            }
        }
        return ipAddress.toString();
    }
}

This example will print something like:

IP Address = 30.30.30.60
IP Address = 142.251.10.113