JScrollPane中JTextArea上的滚动条不起作用

Question

I'm having trouble getting a JTextArea to scroll. I'm not sure how you can mess up a JScrollPane but I seem to have and I just can't see it. It's all part of a larger project but the code below is how I'm creating a JTextArea and adding it to a JScrollPane. When you type beyond the edge of the text area the scrollbar doesn't appear. Setting the vertical scrollbar to always on gives a scrollbar that doesn't do anything.

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

public class TextAreaTest extends JFrame{

    public TextAreaTest() {
     super("Text Area Scroller");

     Container c = getContentPane();

     JTextArea textarea = new JTextArea();
     textarea.setPreferredSize(new Dimension(300, 50));
     textarea.setLineWrap(true);
     textarea.setText("xx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\nxx\n");

     JScrollPane scroller = new JScrollPane(textarea);

     c.add(scroller, BorderLayout.CENTER);
     pack();
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String args[]){
     TextAreaTest instance = new TextAreaTest();
     instance.setVisible(true);
    }
}

I've tried setting the text area text, or rows and columns, in the constructor, neither of which worked. It's doing my head in. Any ideas?

Answer 1

设置滚动窗格的首选大小而不是文本区域。

Answer 2

The others are right about the size. As an aside, consider starting on the Event Dispatch Thread ( EDT ):

public static void main(String args[]) {
    EventQueue.invokeLater(new Runnable() {

        @Override
        public void run() {
            new TextAreaTest().setVisible(true);
        }
    });
}

Answer 3

Use this code

import javax.swing.*;
public class ScrollingTextArea 
{
JFrame f;
JTextArea ta;
JScrollPane scrolltxt;

public ScrollingTextArea() 
{
    // TODO Auto-generated constructor stub

    f=new JFrame();
    f.setLayout(null);
    f.setVisible(true);
    f.setSize(500,500);
    ta=new JTextArea();
    ta.setBounds(5,5,100,200);

    scrolltxt=new JScrollPane(ta);
    scrolltxt.setBounds(3,3,400,400);

    f.add(scrolltxt);

}

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

}