Java 在JPanel上使用GridBagLayout并将JButton放在里面时出现问题

这就是我所知道的.我有两个JPanels，每个都有GridBagLayout.它们的权重x=0.5，并填充两个方向.因此，基本上该窗口是一个JPanel的一半，另一个的一半.而且它应该保持这种状态.但是，如果我将JButton放入其中之一，则JPanel会变宽，并占用第二个JPanel的一些空间.

我应该做些什么来防止这种行为？有没有其他布局可以像我描述的那样工作？

这是我一直在测试的代码.

说

JFrame f = new JFrame();
        f.setLayout(new BorderLayout());
        f.setTitle("Start Window");
        f.setDefaultCloseOperation(f.EXIT_ON_CLOSE);
        f.setSize(400,300);
        f.setResizable(true);

        JPanel top = new JPanel();
        JPanel right = new JPanel();
        JPanel bottom = new JPanel();
        JPanel left = new JPanel();

        top.setPreferredSize(new Dimension(30,30));
        right.setPreferredSize(new Dimension(30,30));
        bottom.setPreferredSize(new Dimension(30,30));
        left.setPreferredSize(new Dimension(30,30));

        f.add(top,BorderLayout.NORTH);
        f.add(right,BorderLayout.EAST);
        f.add(bottom,BorderLayout.SOUTH);
        f.add(left,BorderLayout.WEST);

        JPanel centerContainer = new JPanel(new GridBagLayout());
        GridBagConstraints centerLayout = new GridBagConstraints();
        centerContainer.setBackground(Color.blue);
        f.add(centerContainer);

        JPanel centerLeft = new JPanel(new GridBagLayout());
        GridBagConstraints centerLeftLayout = new GridBagConstraints();
        centerLayout.gridx=0;
        centerLayout.gridy=0;
        centerLayout.weightx=0.5;
        centerLayout.weighty=1;
        centerLayout.fill = GridBagConstraints.BOTH;
        centerLeft.setBackground(Color.red);
        centerContainer.add(centerLeft,centerLayout);

        JPanel centerRight = new JPanel();
        centerLayout.gridx=1;
        centerLayout.gridy=0;
        centerLayout.weightx=0.5;
        centerLayout.weighty=1;
        centerLayout.fill = GridBagConstraints.BOTH;
        centerRight.setBackground(Color.green);
        centerContainer.add(centerRight,centerLayout);

        JPanel leftElement = new JPanel(new GridBagLayout());
        GridBagConstraints leftElementLayout = new GridBagConstraints();

        centerLeftLayout.gridx=0;
        centerLeftLayout.gridy=0;
        centerLeftLayout.weightx=1;
        centerLeftLayout.weighty=1;
        centerLeftLayout.fill = GridBagConstraints.HORIZONTAL;

        centerLeft.add(leftElement,centerLeftLayout);

        JButton leftBtn = new JButton("CLIIIIICK!!!");
        leftBtn.setLayout(new GridBagLayout());
        leftElementLayout.gridx=0;
        leftElementLayout.gridy=0;
        leftElementLayout.weighty=0;
        leftElementLayout.weightx=1;
        leftElementLayout.fill=GridBagConstraints.HORIZONTAL;


        leftElement.add(leftBtn,leftElementLayout);


        f.setVisible(true);

说