如何用java实现计算器运算功能?用到哪些函数?原代码怎么写呀

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class Counter2 extends WindowAdapter
{
static JFrame f=new JFrame("¼ÆËãÆ÷");
static JTextField text1=new JTextField("0.");
static String source="";
static String cal="";
static String object="";
static boolean flag=false;
static boolean flag1=true;
static boolean flag2=false;
public void init()
{
try
{
Container c=f.getContentPane();
JPanel pan1=new JPanel();
JButton b1=new JButton("1");
JButton b2=new JButton("2");
JButton b3=new JButton("3");
JButton b4=new JButton("4");
JButton b5=new JButton("5");
JButton b6=new JButton("6");
JButton b7=new JButton("7");
JButton b8=new JButton("8");