Why isn't my JScrollPane with a JTextArea visible when using null LayoutManager?

Question

I'm trying to display a JTextArea within a JScrollPane, but I just get an empty frame when I run my (simplified) program:

import java.awt.Container;
import java.awt.Dimension;    
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;

public class ScrollPaneTest extends JFrame {
    private Container myCP; 
    private JTextArea resultsTA;
    private JScrollPane scrollPane;

    public ScrollPaneTest() {
        setSize(500, 500);
        setLocation(100, 100);
        myCP = this.getContentPane();
        myCP.setLayout(null);

        resultsTA = new JTextArea("Blah blah");
        scrollPane = new JScrollPane(resultsTA,
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
                JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        scrollPane.setPreferredSize(new Dimension(200, 100));
        scrollPane.setLocation(100, 300);
        myCP.add(scrollPane);

        setVisible(true);
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
    }

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

I use the null LayoutManager to be consistent with the textbook I'm teaching from.

if your textbook insists on null LayoutManager more often than to teach the manual positioning and sizing once (and by that showing huch much work it is, as you experience :-) throw it into the bin - it's useless ;-) A so-called null-layout is a no-no-never — kleopatra, Apr 07 '11 at 07:53
The textbook is by a senior member of my department and good friend. :-) I'm just teaching the course for her this once. — Ellen Spertus, Apr 07 '11 at 13:50

Harry Joy · Accepted Answer · 2011-04-07T06:11:11.127

This will work:

public class ScrollPaneTest extends JFrame {
    private Container myCP; 
    private JTextArea resultsTA;
    private JScrollPane scrollPane;

    public ScrollPaneTest() {
        setSize(500, 500);
        setLocation(100, 100);
        myCP = this.getContentPane();
        myCP.setLayout(null);

        resultsTA = new JTextArea("Blah blah");
        resultsTA.setBounds(10, 10, 150, 30);

        scrollPane = new JScrollPane(resultsTA,JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        scrollPane.setPreferredSize(new Dimension(200, 100));
        scrollPane.setBounds(0, 0, 500, 500);

        myCP.add(scrollPane);
        setVisible(true);
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
    }

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

If you are using null layout then you must specify bounds.

Edit

setBounds() method coveres the task of setLocation() method.

for example, setBounds(x,y,w,h);

first 2 will set the x/y location of that component with respect to its container. second 2(w/h) will set the size of that component.

in other words:-

setBounds(int x, int y, int witdh, int height) – Sets the component’s size and location
setLocation(int x, int y) – Sets the component’s location

The problem is you need to specify the textarea size and bounds, not only for the scrollpane, as stated. — David Oliván, Apr 07 '11 at 05:47
Could someone clarify the meaning of setBounds()? The API isn't clear how this differs from setLocation(). Thanks. — Ellen Spertus, Apr 07 '11 at 05:59

score 1 · Answer 2 · answered Apr 07 '11 at 13:13

I have to agree with kleopatra's comment on this one.

Here is a variant of Harry Joy's code that uses layouts. It appears on-screen almost the same size as the original GUI but is resizable. It will also adapt easily to different PLAFs, default font sizes etc. (though it might end up a different size on-screen), whereas something with a null layout will not.

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

public class ScrollPaneTest extends JFrame {
    private Container myCP;
    private JTextArea resultsTA;
    private JScrollPane scrollPane;

    public ScrollPaneTest() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocation(100, 100);
        myCP = this.getContentPane();

        resultsTA = new JTextArea("Blah blah", 28, 43);

        scrollPane = new JScrollPane(resultsTA,JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);

        myCP.add(scrollPane);
        setVisible(true);
        pack();
    }

    public static void main(String[] args) {
        Runnable r = new Runnable() {
            public void run() {
                new ScrollPaneTest();
            }
        };
        SwingUtilities.invokeLater(r);
    }
}

I hadn't known about setDefaultCloseOperation() or pack(), both of which will be very useful to me. Thank you. — Ellen Spertus, Apr 09 '11 at 15:09

Why isn't my JScrollPane with a JTextArea visible when using null LayoutManager?

2 Answers2