java swing 窗口布局

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class AppleExpertSystem {
    public static void main(String[] args) {
        AppleMainFrame aesFrame = new AppleMainFrame("系统");
        aesFrame.setVisible(true);
    }
}

class AppleMainFrame extends JFrame implements ActionListener {
    Container p;
    final JScrollPane leftPane;                   //放目录树面板
    final JScrollPane rightPane;                  //主面板
    final JSplitPane jsp;                         //分割窗口
    final JPanel treePane = new JPanel();
    final JPanel mainPane = new JPanel();
    int V_SBar = ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS;
    int H_SBar = ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS;

    final JMenuBar mb = new JMenuBar();
    final JMenu[] m = {new JMenu("开始"),
                                         new JMenu("决策"),
                                         new JMenu("视图"),
                                         new JMenu("帮助")};
    final JMenuItem[][] mi = {{new JMenuItem("功能"),new JMenuItem("退出")},
                                {new JMenuItem("")},
                                {new JMenuItem("")},
                                {new JMenuItem("使用帮助"),new JMenuItem("关于")}};
    public AppleMainFrame(String title) {
        super(title);
        setSize(800, 600);
        centerOnScreen();
        p = getContentPane();
        for(int i=0; i<m.length; i++) {
      for(int j=0; j<mi[i].length; j++) {
        m[i].add(mi[i][j]);
        mi[i][j].addActionListener(this);
      }
      mb.add(m[i]);
    }
        setJMenuBar(mb);
        treePane.add(new JTextArea("left"));
        mainPane.add(new JTextArea("right"));
        leftPane = new JScrollPane(treePane, V_SBar, H_SBar);
        rightPane = new JScrollPane(mainPane, V_SBar, H_SBar);
        jsp = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, leftPane, rightPane);
        Dimension winSize = getSize();
        jsp.setDividerLocation(winSize.width/6);
        jsp.setDividerSize(5);
        p.add(jsp);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public void actionPerformed(ActionEvent e) {
    }

    public void centerOnScreen() {        //使窗体被创建后在屏幕中间显示
        Dimension displaySize = getToolkit().getScreenSize();
        Dimension winSize = getSize();
        int x = (displaySize.width - winSize.width) / 2;
        int y = (displaySize.height - winSize.height) / 2;
        if(x < 0) {
            x = 0;
        }
        if(y < 0) {
            y = 0;
        }
        setLocation(x, y);
    }
}