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

public class exam3 extends JFrame implements ActionListener{
    JScrollPane helpSP;//帮助面板
    JTextArea helpTA;//帮助文本框
    JPanel p1,p2;
    JButton b1,b2;//计算结果的按钮
    JTextField tf1,tf2,tf3,tf4,tf5,tf6;
    JLabel l1,l2,l3,l4;
    String s1,s2,s3,s4;
    int end1;
    int end2;
    public exam3() {
        JMenuBar mb = new JMenuBar();//创建菜单条
        setJMenuBar(mb);
        //创建菜单
        JMenu fileM = new JMenu("文件");
        JMenu helpM = new JMenu("帮助");
        //将菜单添加到菜单条
        mb.add(fileM);
        mb.add(helpM);
        //创建菜单项
        JMenuItem file1M = new JMenuItem("退出");
        JMenuItem help1M = new JMenuItem("帮助");
        //将菜单项加入菜单中
        fileM.add(file1M);
        helpM.add(help1M);
        //注册监听器
        file1M.addActionListener(this);
        help1M.addActionListener(this);
        
        //帮助面板代码
        helpTA = new JTextArea(5,10);
        helpSP = new JScrollPane(helpTA);
        helpTA.setEditable(false);
        helpTA.append("执行简单计算\n");
        helpTA.append("1.  键入计算的第一个数字。\n");
        helpTA.append("2.  单击“+”执行加、“*”执行乘。\n");
        helpTA.append("3.  键入计算的下一个数字。\n");
        helpTA.append("4.  单击“=”。\n");
        //计算器界面代码
        p1 = new JPanel();
        p2 = new JPanel();
        b1 = new JButton("计算");
        b2 = new JButton("计算");
        tf1 = new JTextField();
        tf2 = new JTextField();
        tf3 = new JTextField();
        tf4 = new JTextField();
        tf5 = new JTextField();
        tf6 = new JTextField();
        l1 = new JLabel("+");
        l2 = new JLabel("=");
        l3 = new JLabel("+");
        l4 = new JLabel("=");
        p1.setLayout(new GridLayout(1,6));
        p1.add(tf1);
        p1.add(l1);
        p1.add(tf2);
        p1.add(l2);
        p1.add(tf3);
        p1.add(b1);
        p2.setLayout(new GridLayout(1,6));
        p2.add(tf4);
        p2.add(l3);
        p2.add(tf5);
        p2.add(l4);
        p2.add(tf6);
        p2.add(b2);
        add(p1,"South");
        add(p2,"North");
        pack();//调整大小 其他也跟着大小
        
        
        
        
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//关闭窗口
    }
    //监听器代码
    public void actionPerformed(ActionEvent e) {
        Object temp = e.getSource();
        //"+"号操作
        
        if(temp == b1) {
            int s1 = Integer.parseInt(tf1.getText());
            int s2 =Integer.parseInt(tf2.getText());
            end1 = s1 + s2;
            tf3.setText("end1");
        }
        
        //"-"号操作
        //退出按钮
        if(e.getActionCommand().equals("退出")) {
            dispose();
            System.exit(0);
        }
        //帮助按钮
        if(e.getActionCommand().equals("帮助")) {
            JOptionPane.showMessageDialog(this, helpSP);
        }
    }
    public static void main(String[] args) {
        exam3 e3 = new exam3();//面板代码
        e3.setTitle("简单计算器");
        e3.setBounds(300,200,400,400);
        e3.setResizable(false);
        e3.setVisible(true);
    }
}

//帮助面板代码
        helpTA = new JTextArea(5,10);
        helpSP = new JScrollPane(helpTA);
        helpTA.setLineWrap(true);//隐藏滚动条
        helpTA.setEditable(false);
        helpTA.append("执行简单计算\n");
        helpTA.append("1.  键入计算的第一个数字。\n");
        helpTA.append("2.  单击“+”执行加、“*”执行乘。\n");
        helpTA.append("3.  键入计算的下一个数字。\n");
        helpTA.append("4.  单击“=”。\n");

布局改一改，实现计算就行了，
其他没什么要改的，功能不多。
自己多试试吧！