Automatically Expanding using JTabbedPane

Question

I'm trying to get the JTabbedPane automatically expanding over the parent JPanel.

When I put everything in the Main class, it works:

Main:

public class Main extends JFrame {

    public Main() {
        JTabbedPane tpane = new JTabbedPane();
        JPanel panel = new JPanel();
        panel.add(new JButton("Button 1"));
        tpane.addTab("Tab1", panel);

        JPanel panel2 = new JPanel();
        panel2.add(new JButton("Button 2"));
        tpane.addTab("Tab2", panel2);

        this.setSize(500, 500);
        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.add(tpane);
        this.setVisible(true);
    }

    public static void main(String[] args) {
        Main m = new Main();
    }
}

But when I put it into another class, it won't work anymore:

Main:

public class Main extends JFrame {

    View view = new View();

    public Main() {
        this.setSize(500, 500);
        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.add(view, BorderLayout.CENTER); // BorderLayout
        this.setVisible(true);
    }

    public static void main(String[] args) {
        Main m = new Main();
    }
}

View:

public class View extends JPanel {

    public View() {
        JTabbedPane tpane = new JTabbedPane();
        JPanel panel = new JPanel();
        panel.add(new JButton("Button 1"));
        tpane.addTab("Tab1", panel);

        JPanel panel2 = new JPanel();
        panel2.add(new JButton("Button 2"));
        tpane.addTab("Tab2", panel2);

        this.add(tpane, BorderLayout.CENTER); // BorderLayout
    }
}

score 1 · Accepted Answer · edited Jun 20 '20 at 09:12

The frame has a border layout, the panel has a flow layout.

A component added to a border layout with no constraint ends up in the CENTER & will be stretched to the available height and width.
A component added to a flow layout will maintain its natural size.

More generally, don't set the size of a top level container. It is better to call pack() which will make the TLC the exact size needed to accommodate the components within. To add white space to a GUI, use layout constraints (not especially relevant when the layout only has a single component), or borders. See this answer for a working example.

Edit

I set a BorderLayout to both, Main and View. But the result remained the same.

This is the result of changing the layout of the View as seen here.

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

public class Main extends JFrame {

    View view = new View();

    public Main() {
        this.setSize(500, 500);
        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.add(view);
        this.setVisible(true);
    }

    public static void main(String[] args) {
        Main m = new Main();
    }
}

class View extends JPanel {

    public View() {
        super(new BorderLayout()); // Just 1 line difference!
        JTabbedPane tpane = new JTabbedPane();
        JPanel panel = new JPanel();
        panel.add(new JButton("Button 1"));
        tpane.addTab("Tab1", panel);

        JPanel panel2 = new JPanel();
        panel2.add(new JButton("Button 2"));
        tpane.addTab("Tab2", panel2);

        this.add(tpane);
    }
}

I set a `BorderLayout` to both, `Main` and `View`. But the result remained the same. Please see my update. — Evgenij Reznik, Mar 12 '17 at 12:45
*"But the result remained the same."* Not here. Please see the update to my answer. — Andrew Thompson, Mar 12 '17 at 13:12
Now it works, thank you. But why it doesn't work, when setting a `BorderLayout` like in my example? — Evgenij Reznik, Mar 12 '17 at 13:27
Change (in the 2nd example edit) `this.add(tpane, BorderLayout.CENTER); // BorderLayout` to (not tested) `System.out.println("Layout is: " + this.getLayout()); this.add(tpane, BorderLayout.CENTER); // BorderLayout`. If you cannot figure it out from the result, get back to me.. — Andrew Thompson, Mar 12 '17 at 14:19

Automatically Expanding using JTabbedPane

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