java - JTextArea expands dynamically (undesired)

Question

Something strange occured. I have a text area and a button. When I type text into the area, the button starts moving! Please see attached code. I tried adding more layers of panels and setting component alignments, but it still happens.

class MyFrame extends JFrame {
...
public MyFrame() {
    super("example");
    JPanel panel = new JPanel();
    panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
    add(panel);

    JTextArea _textArea = new JTextArea();
    _textArea.setSize(800, 600);
    panel.add(_textArea);

    JButton btn = new JButton("Send");
    panel.add(btn);

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(1000, 800);
    setVisible(true);
    }
}

whats the mystery all about? how does one component affects the other?

Answer 1

BoxLayout is a lot more complicated than BorderLayout, which is what you need. BorderLayout uses general directions like NORTH, EAST, SOUTH, and WEST, which is very simple. Here's the easy way to get what you're looking for:

class MyFrame extends JFrame {
    //...
    public MyFrame() {
        super("Example");   
        JTextArea textArea = new JTextArea();
        textArea.setSize(800, 600);
        add(textArea, BorderLayout.CENTER);

        JButton btn = new JButton("Send");
        add(btn, BorderLayout.SOUTH);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(1000, 800); 
        setVisible(true);
    }
}

A lot shorter too.