JScrollPane没有在我的JTextArea上工作？

Question

I'm not very familiar with java GUIs and layouts but I gotta admit, I didn't think it would be this tricky! I'm not quite sure what I'm doing here.

I merely want to add 2 textareas ontop of each other and add a jscrollpane to each of them. But I can't get the JScrollPanes to work. Here's how I currently got it.

public class Class extends JFrame {

     public Class() {
    super("Title");

    getContentPane().setLayout(
            new BoxLayout(getContentPane(), BoxLayout.Y_AXIS));
    setResizable(false);

    JTextArea window1 = new JTextArea("text");
    window1.setEditable(false);
    window1.setBorder(BorderFactory.createLineBorder(Color.BLACK));
    window1.setPreferredSize(new Dimension(200, 250));
    window1.setLineWrap(true);

    add(window1);

    JScrollPane scroll = new JScrollPane(window1);
    scroll.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
    scroll.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);

    add(scroll);

    JTextArea window2 = new JTextArea();
    window2.setEditable(true);
    window2.setBorder(BorderFactory.createLineBorder(Color.BLACK));
    window2.setPreferredSize(new Dimension(100, 50));
    window2.setLineWrap(true);
    add(window2);

    setDefaultCloseOperation(EXIT_ON_CLOSE);
    pack();
    setVisible(true);
}
}

It looks good, there's a box with "text" and right of it there's the scrollpane. Below them both there's the second JTextArea (no scrollpane yet). The problem is that when I write text in window 1 and the text goes below, outside of the jtextarea, I expected the JScrollPane to actually be scrollable so I could scroll down to see the text at the bottom but nothing happens when I press it (and it doesn't change in size or anything either). Anything noticable I've missed?

Answer 1

The problem is that when I write text in window 1 and the text goes below, outside of the jtextarea, I expected the JScrollPane to actually be scrollable

---

JTextArea has been included to JScrollPane . You should not add window1 .

add(window1);// Remove this.

JScrollPane scroll = new JScrollPane(window1);//here you added window1
add(scroll);// This statement also added the JTextArea 
            //and do the operaton of above add.

Answer 2

You add your JTextArea to JScrollPane you needn't to add it to your JFrame . Also setPreferedSize() use for JScrollPane , instead of directly to JTextArea , because your JTextArea will be not scrollable. I have changed your code, try it:

public class Class  extends JFrame {
    public Class () {
        super("Title");

        getContentPane().setLayout(
                new BoxLayout(getContentPane(), BoxLayout.Y_AXIS));
        setResizable(false);

        JTextArea window1 = new JTextArea("text");
        window1.setEditable(false);
        window1.setBorder(BorderFactory.createLineBorder(Color.BLACK));
        window1.setLineWrap(true);


        JScrollPane scroll1 = new JScrollPane(window1);
        scroll1.setPreferredSize(new Dimension(200, 250));
        scroll1.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
        scroll1.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
        add(scroll1);

        JTextArea window2 = new JTextArea();
        window2.setEditable(true);
        window2.setBorder(BorderFactory.createLineBorder(Color.BLACK));
        window2.setLineWrap(true);
        add(window2);

        JScrollPane scroll2 = new JScrollPane(window2);
        scroll2.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
        scroll2.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
        scroll2.setPreferredSize(new Dimension(100, 50));
        add(scroll2);

        setDefaultCloseOperation(EXIT_ON_CLOSE);
        pack();
        setVisible(true);
    }

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