How do I change JTabbedPane tab placement position?

By Wayan in Swing 0 Comment

By default, the tabs in a JTabbedPane component is placed on the top. But you can place the tabs on every side of the JTabbedPane component, for example it can be on the top, on the right, on the left or on the bottom of the JTabbedPane.

To change the tab placement position you need to set the tab placement when creating an instance of JTabbedPane. The tab placement can be set using the following constant values: JTabbedPane.TOP, JTabbedPane.RIGHT, JTabbedPane.LEFT and JTabbedPane.BOTTOM.

Let’s see the following code snippet to demonstrate it.

package org.kodejava.swing;

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

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

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

        JFrame frame = new JFrame("Tabbed Pane Tab Placement Demo");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

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

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

        // Creates a JTabbedPane with tabs at the bottom.
        JTabbedPane pane = new JTabbedPane(JTabbedPane.BOTTOM);
        pane.addTab("Tab 1", createPanel("Panel 1"));
        pane.addTab("Tab 1", createPanel("Panel 2"));
        pane.addTab("Tab 3", createPanel("Panel 3"));

        this.add(pane, BorderLayout.CENTER);
    }

    private JPanel createPanel(String title) {
        JPanel panel = new JPanel();
        panel.setLayout(new BorderLayout());
        panel.add(new JLabel(title), BorderLayout.NORTH);
        return panel;
    }
}

And here is the result of the code snippet above.

JTabbedPane Tab Position Demo

How do I detect tab selection changes in JTabbedPane?

By Wayan in Swing 0 Comment

In this example you will learn how to detect tab selection changes in a JTabbedPane component. To get notified when a tab is selected you must add a ChangeListener to the JTabbedPane component using the addChangeListener(). This method take an instance of class that implements the ChangeListener interface as its arguments.

In this example we implement the ChangeListener interface in the TabbedPaneSelection class. And we need to create an implementation for the stateChanged() method as defined by this interface contract. By implementing the interface in the TabbedPaneSelection class, we don’t need to create a separate class that specifically implement this interface. That’s why in the code snippet below we just pass the current object, using the this keyword, when calling the addChangeListener() method.

The stateChanged() method of this interface will be fired every time a new tab is selected. To get the selected tab index you can use the JTabbedPane‘s getSelectedIndex() method. The index returned by the getSelectedIndex() method is zero based, it means that if you select the first tab you will get index of 0, and if you select the second tab you will get index of 1.

package org.kodejava.swing;

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

public class TabbedPaneSelection extends JPanel implements ChangeListener {
    public TabbedPaneSelection() {
        initializeUI();
    }

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

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

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

    private void initializeUI() {
        JTabbedPane tabbedPane = new JTabbedPane();

        JPanel dashboardPanel = new JPanel();
        tabbedPane.addTab("Dashboard", dashboardPanel);

        JPanel accountPanel = new JPanel();
        tabbedPane.addTab("Account", accountPanel);

        this.setLayout(new BorderLayout());
        this.setPreferredSize(new Dimension(500, 200));
        this.add(tabbedPane, BorderLayout.CENTER);

        // Add ChangeListener to the tabbed pane.
        tabbedPane.addChangeListener(this);
    }

    public void stateChanged(ChangeEvent e) {
        JTabbedPane tabbedPane = (JTabbedPane) e.getSource();
        int selectedIndex = tabbedPane.getSelectedIndex();
        JOptionPane.showMessageDialog(null, "Selected Index: " + selectedIndex);
    }
}

If you run the presented code snippet above you’ll get the output as shown in the image below. And if you click the tab a message dialog will be displayed showing you the selected index.

JTabbedPane Selection Demo

How do I create a simple JTabbedPane?

By Wayan in Swing 0 Comment

In this example you will learn how to use JTabbedPane to arrange some components in tabbed view. The JTabbedPane component of the Swing API allows some components such as panels to share the same view. By selecting the corresponding tab, the panel will be displayed on the user’s screen. To add tabs to the JTabbedPane class you can use the addTab() method.

To the addTab() method accept two arguments, the title of the tab and the component you wish to display as the content of the tab. In the code snippet below we will use a simple panel as the content of the tab. You can also define an image icon for the tab which makes the program looks better. You can read it in this example:

Now, let’s create a simple example of JTabbedPane which has three tabs and the corresponding content, they are the Dashboard, Transaction and Account tabs. Below is an image that show how the screen will look.

Simple JTabbedPane Demo

package org.kodejava.swing;

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

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

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

        JFrame frame = new JFrame("Simple Tabbed Pane Demo");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

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

    private void initializeUI() {
        JTabbedPane tabbedPane = new JTabbedPane();

        JPanel dashboardPanel = new JPanel();
        dashboardPanel.add(new JLabel("Dashboard"));

        // Add Dashboard Tab
        tabbedPane.addTab("Dashboard", dashboardPanel);

        JPanel transactionPanel = new JPanel();
        transactionPanel.add(new JLabel("Transaction"));

        // Add Transactions Tab
        tabbedPane.addTab("Transaction", transactionPanel);

        JPanel accountPanel = new JPanel();
        accountPanel.add(new JLabel("Account"));

        // Add Account Tab
        tabbedPane.addTab("Account", accountPanel);

        this.setLayout(new BorderLayout());
        this.setPreferredSize(new Dimension(500, 200));
        this.add(tabbedPane, BorderLayout.CENTER);
    }
}

How do I invoke superclass constructor?

By Wayan in Basic, Core API 0 Comment

This example shows you how to use the super keyword to call a superclass constructor. The Female class constructor calls its superclass constructor and initializes its own initialization parameters. The call to the superclass constructor must be done in the first line of the constructor in the subclass.

package org.kodejava.example.fundamental;

public class Human {
    private String gender;
    private int age;

    public Human(String gender) {
        this.gender = gender;
    }
}

To call a superclass constructor we call super(). In the case below we call the superclass constructor with one string variable as a parameter.

package org.kodejava.example.fundamental;

public class Female extends Human {
    private String hairStyle;

    public Female(String hairStyle, String gender) {
        super(gender);
        this.hairStyle = hairStyle;
    }
}

How do I create and implement abstract class?

By Wayan in Basic, Core API 0 Comment

Abstract class is a class that have one or more methods declared, but not defined. Abstract class cannot have instances. This class uses in inheritance to take advantage of polymorphism. To declare that a class is abstract, use the abstract keyword in front of the class keyword in the class definition.

Methods in abstract class that have no definition are called abstract methods. The declaration for an abstract method ends with a semicolon and you specify the method with the abstract keyword to identify it as such. The implementation is left to the sub classes.

package org.kodejava.example.fundamental;

public abstract class Animal {
    private String species;

    public Animal(String species) {
        this.species = species;
    }

    public abstract void makeASound();

    public String getSpecies() {
        return species;
    }

    public static void main(String[] args) {
        Animal pig = new Pig("Warthog");
        pig.makeASound();
    }
}

The Pig class extends the Animal class. Because the Animal class contains an abstract method makeASound() the Pig class must implements this method or else the Pig will also become an abstract class.

package org.kodejava.example.fundamental;

public class Pig extends Animal {

    public Pig(String species) {
        super(species);
    }

    @Override
    public void makeASound() {
        System.out.println("oink oink");
    }
}