Java大小调整JPanel和JPanel组件

Question

I'm trying to build a GUI in Java Swing. I have alot of trouble sizing components. I managed to size a JPanel by setting the dimensions with setPreferredSize() , but I can't get the components within that JPanel to size properly.

This is my screen with only the JPanel visible.

When I add the button to my JPanel the following happens:

As you can see the button is taking up the whole lenght and width of my JPanel/JFrame. Why is this happening? How can I fix it?

Here is my code:

Application.java

public void start() {
    ControllerObserveer observeer = new ControllerObserveer();

    frame = new JFrame("-");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
    frame.setLayout(new BorderLayout());
    frame.add(observeer.getView(), BorderLayout.CENTER);
    frame.setResizable(false);
}

ControllerObserveer.java

public class ControllerObserveer {
    private ModelObserveer model;
    private ViewObserveer view; 

    public JPanel getView(){
        return this.view.p;
    }
}

ViewObserveer.java

public class ViewObserveer {

    public JPanel p;

    public ViewObserveer(){
        this.p = new JPanel(new BorderLayout(), false);
        p.setPreferredSize(new Dimension(500, 500));
        p.setBackground(Color.red);

        JButton b = new JButton("Hello World!");
        b.setPreferredSize(new Dimension(40, 40));

        p.add(b);

    }
}

At last I would like to ask what the diffrences are between the diffrent layouts, like BorderLayout() or BoxLayout() for example.

Thank you for your time!

Answer 1

Install Java WindowBuilder on Eclipse. So, you can get things done.. "but I can't get the components within that JPanel to size properly."