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 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 create a vertical JSlider?

By I Wayan Saryada in Swing 0 Comment

To create a vertical JSlider set the orientation on the JSlider‘s constructor to JSlider.VERTICAL. If you do not pass JSlider.VERTICAL as a constructor parameter use the setOrientation() method instead.

package org.kodejava.swing;

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

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

    public static void showFrame() {
        JPanel panel = new JSliderVertical();
        panel.setOpaque(true);

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

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

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

        // Creates a vertical JSlider that accept value in the
        // range between 0 and 20. The initial value is set to 4.
        JSlider slider = new JSlider(JSlider.VERTICAL, 0, 20, 4);
        slider.setPaintTicks(true);
        slider.setPaintLabels(true);
        slider.setMinorTickSpacing(1);
        slider.setMajorTickSpacing(4);

        add(slider, BorderLayout.CENTER);
    }
}

The screen capture of the code snippet above.

Vertical JSlider Demo

How do I use a JSlider component?

By I Wayan Saryada in Swing 0 Comment

This simple example show you how to use the JSlider component. A JSlider component is intended to let the user easily enter a numeric value bounded by a minimum and maximum value.

There are a couples properties that you need to set when creating a JSlider. These include setting setMinorTickSpacing(), setMajorTickSpacing(), setPaintTicks() and setPaintLabels(). These methods set the minor tick spacing, major tick spacing, display the ticks and the tick labels.

To get the selected value from JSlider we need to implements the stateChanged() method defined in the ChangeListener interface and then pass the listener to the JSlider by calling the addChangeListener() method.

package org.kodejava.swing;

import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import java.awt.*;

public class JSliderDemo extends JPanel implements ChangeListener {
    private JTextField field;

    public JSliderDemo() {
        initializeUI();
    }

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

        // Creates an instance of JSlider with a horizontal
        // orientation. Define 0 as the minimal value and
        // 50 as the maximum value. The initial value is set
        // to 10.
        JSlider slider = new JSlider(JSlider.HORIZONTAL, 0, 50, 10);

        slider.setPaintTicks(true);
        slider.setPaintLabels(true);
        slider.setMinorTickSpacing(1);
        slider.setMajorTickSpacing(10);

        slider.addChangeListener(this);

        JLabel label = new JLabel("Selected Value:");
        field = new JTextField(5);

        JPanel panel = new JPanel();
        panel.setLayout(new FlowLayout());
        panel.add(label);
        panel.add(field);

        add(slider, BorderLayout.NORTH);
        add(panel, BorderLayout.SOUTH);
    }

    public void stateChanged(ChangeEvent e) {
        JSlider slider = (JSlider) e.getSource();

        // Get the selection value of JSlider
        field.setText(String.valueOf(slider.getValue()));
    }

    public static void showFrame() {
        JPanel panel = new JSliderDemo();
        panel.setOpaque(true);

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

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JSliderDemo.showFrame();
            }
        });
    }
}

Below is the result of the code snippet above.

JSlider Demo

How do I create a scrollable JTable component?

By I Wayan Saryada in Swing 1 Comment

To create a scrollable JTable component we have to use a JScrollPane as the container of the JTable. Besides, that we also need to set the table auto resize mode to JTable.AUTO_RESIZE_OFF so that a horizontal scroll bar displayed by the scroll pane when needed. If we do not turn off the auto resize mode, the columns of the table will be resized to fit the available window size.

package org.kodejava.swing;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import java.awt.BorderLayout;
import java.awt.Dimension;

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

    private static void showFrame() {
        JPanel panel = new ScrollableJTable();
        panel.setOpaque(true);

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setTitle("Scrollable JTable");
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

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

    private void initializeUI() {
        setLayout(new BorderLayout());
        setPreferredSize(new Dimension(500, 250));

        JTable table = new JTable(20, 20);

        // Turn off JTable's auto resize so that JScrollPane will show a horizontal
        // scroll bar.
        table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);

        JScrollPane pane = new JScrollPane(table);
        add(pane, BorderLayout.CENTER);
    }
}

Below is the result of the code snippet above.

Scrollable JTable Component Demo

Scrollable JTable Component Demo