JTextArea doesn't work when Frame is split in two JPanel

Question

I want split my Frame into two JPanel and the right JPanel serve as a textarea used to input and display. However, I can't input anything in it and it can't display any thing. the code as below:

JPanel jp1, jp2;
public DemoFrame() {
    jp1 = new JPanel();
    jp2 = new JPanel();
    JLabel label = new JLabel("text");
    JTextArea ta = new JTextArea(100,100);
    ta.setText("some text");
    ta.setSize(300, 300);
    jp2.add(label);
    jp2.add(ta);
    JSplitPane jsp = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, jp1, jp2);
    this.getContentPane().add(jsp);;
    setBounds(300, 200, 500, 500);
    setVisible(true);
    jsp.setDividerLocation(0.5);// 
}

the output as below(it doesnt display anything):

For better help sooner, post a [MCVE] or [Short, Self Contained, Correct Example](http://www.sscce.org/). — Andrew Thompson, Mar 16 '18 at 08:26
`JTextArea ta = new JTextArea(10, 10);` should begin to hint at the mistake.. Note that the two integers passed to the constructor are not pixels, but columns and rows. — Andrew Thompson, Mar 16 '18 at 08:30
@ Hovercraft Full Of Eels Yeah, I get it. Thank you very much. — nail fei, Apr 14 '18 at 13:49

score 4 · Accepted Answer · answered Mar 16 '18 at 09:38

Congratulations, you've fallen victim to a number of conspiring issues.

The main culprit is FlowLayout, which is the default layout manager for JPanel. Essentially, when you add your, rather large, JTextArea to the panel, the FlowLayout is trying to honour the preferred size as best as it can within the constraints of the available space. For reasons I'm not 100% sure of, that means laying out the component beyond the visible bounds of the container.

If you type enough text, you will begin to see it.

While there are a number of ways you might fix this, they are basically the same solution - use a different layout manager.

For this example, I've just used a BorderLayout instead

import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTextArea;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

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

    private JPanel jp1, jp2;

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }
                jp1 = new JPanel();
                jp2 = new JPanel(new BorderLayout());
                JLabel label = new JLabel("text");
                JTextArea ta = new JTextArea(50, 50);
                ta.setText("some text");
                jp2.add(label, BorderLayout.NORTH);
                jp2.add(new JScrollPane(ta));
                JSplitPane jsp = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, jp1, jp2);

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(jsp);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}

JTextArea doesn't work when Frame is split in two JPanel

1 Answers1