滚动条没有出现

Question

I have added some code for scrollbar which I got from questions asked by some other people on stackoverflow but I am not getting any scrollbar added to my JTextArea. I want to add scrollbar to JTextArea area2 in f2 frame.

import javax.swing.*;
import java.io.*;
import java.awt.event.*;
public class TextAreaExample implements ActionListener {
    JFrame f1 = new JFrame("INPUT WINDOW");
    JFrame f2 = new JFrame("FILE DATA OUTPUT");
    JTextArea area1;
    JTextArea area2;
    JButton b;
    TextAreaExample() {
        area1 = new JTextArea();
        area2 = new JTextArea();
        JScrollPane scroll = new JScrollPane (area2, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        b = new JButton("click Me");
        b.setBounds(100, 95, 80, 30);
        f1.add(b);

        area1.setBounds(10, 30, 200, 60);
        area2.setBounds(5, 5, 480, 480);
        f1.add(area1);
        f2.add(area2);
        f2.add(scroll);
        f1.setSize(300,140);
        f2.setSize(510, 510);  
        f1.setLayout(null);
        f2.setLayout(null);
        f1.setVisible(true);
        f2.setVisible(true);
        b.addActionListener(this);
        f1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f2.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    public void actionPerformed(ActionEvent e) {
        if(e.getSource() == b) {
            String s1 = area1.getText();

            String s2 = "";
            try {
                FileInputStream fin = new FileInputStream(s1);
                BufferedInputStream bin = new BufferedInputStream(fin);
                int i;
                while((i = bin.read()) != -1) {
                     s2 = s2 + (char)i;
                }
                bin.close();
                fin.close();
            }catch(Exception a) {
                System.out.println(a);
            }
            area2.setText(s2);
        }
    }
    public static void main(String args[]) {  
        new TextAreaExample();

    }
}

Answer 1

    JScrollPane scroll = new JScrollPane (area2, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
    b = new JButton("click Me");
    b.setBounds(100, 95, 80, 30);
    f1.add(b);

    area1.setBounds(10, 30, 200, 60);
    area2.setBounds(5, 5, 480, 480);
    f1.add(area1);
    f2.add(area2);

First you create a JScrollPane using the JTextArea as a parameter, which is correct.

But then you add the text area to the frame, which is incorrect. Swing components can only have a single parent so the text area is removed from the scroll pane.

The scroll pane must be added to the frame.

f1.add(scroll);

Also, get rid of all the null layouts and setBounds() statements. Swing was designed to be used with layout managers. Read the section from the Swing tutorial on Layout Manager for more information and examples to get your started.

Now when you create the text area you can use:

JTextArea textArea = new JTextArea(5, 20);

to suggest the original size for the text area. Scrollbars will then appear when more than 5 lines of data is added.