我们如何在java中的JTextArea上添加JScrollPane？

Question

Can anybody tell me what is the problem in following program? I want to fit JScrollPane on JtextArea but when I add it then JTextArea is not visible.

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

class Area extends JFrame
{
    private JTextArea ta;
    private JTextField tf;
    JScrollPane jp;

    public Area()
    {
       super("Text Area");
       tf=new JTextField();
       tf.setBounds(100,350,300,30);
       add(tf);
       ta=new JTextArea();
       ta.setBounds(100,100,300,200);
       jp= new JScrollPane(ta);
       add(jp);
       setLayout(null);
       setSize(500,500);
       setVisible(true);
       setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   }

   public static void main(String...s)
   {
      new Area();
   }
}

Answer 1

I see several problems:

• Don't use a null layout; do use a real layout .

• The default layout of JFrame is BorderLayout ; the default position is CENTER ; only one component can occupy a position at a time; the example below uses NORTH & CENTER .

• Use the appropriate constructor parameters to size the text components initially.

• The scrollbar will appear automatically whenever the scrollpane is smaller than the enclosed component; resize the frame to see the effect.

• As shown here , the frame's size is made smaller for effect.

• See also Initial Threads .

import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;

/** @see https://stackoverflow.com/a/19215436/230513 */
public class Area extends JFrame {

    public Area() {
        super("Text Area");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JTextField tf = new JTextField(12);
        add(tf, BorderLayout.NORTH);
        JTextArea ta = new JTextArea(24, 12);
        JScrollPane jp = new JScrollPane(ta);
        add(jp, BorderLayout.CENTER);
        pack();
        // arbitrary size to make vertical scrollbar appear
        setSize(240, 240);
        setLocationByPlatform(true);
        setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Area();
            }
        });
    }
}

Answer 2

Try this:

public Area()
{
   super("Text Area");
   tf=new JTextField();
   tf.setBounds(100,350,300,30);
   add(tf);
   ta=new JTextArea();
   jp= new JScrollPane(ta);
   jp.setBounds(5, 5, 100, 100);
   add(jp);
   setLayout(null);
   setSize(500,500);
   setVisible(true);
   setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

You have to use setBounds on JScrollPane, not on JTextArea

Answer 3

sounds like its added but its not shown because of the policy try this:

  jp.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
  jp.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);