简单计算器 (加 减 乘 除 清零)

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Stack;

import javax.swing.JApplet;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Count extends JApplet implements ActionListener
{
	
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	private JTextField textField = new JTextField("请输入");
	String operator = "";//操作
	String input = "";//输入的 式子
	boolean flag =  true;
//	boolean flag1 = true;
//	boolean flag2 = true;
	public void init()//覆写Applet里边的init方法
	{
		Container C = getContentPane();
		JButton b[] = new JButton[16];
		JPanel panel = new JPanel();
		C.add(textField, BorderLayout.NORTH);
		C.add(panel,BorderLayout.CENTER);
		panel.setLayout(new GridLayout(4, 4,5,5));
		String name[]={"7","8","9","+","4","5","6","-","1","2","3","*","0","C","=","/"};//设置 按钮
		for(int i=0;i<16;i++)//添加按钮
		{
			b[i] = new JButton(name[i]);
			b[i].setBackground(new Color(192,192,192));
			b[i].setForeground(Color.BLUE);//数字键 设置为 蓝颜色
			if(i%4==3)
				b[i].setForeground(Color.RED);
			b[i].setFont(new Font("宋体",Font.PLAIN,16));//设置字体格式
			panel.add(b[i]);
			b[i].addActionListener(this);
		}
		b[13].setForeground(Color.RED);//非数字键，即运算键设置为红颜色
		b[13].setForeground(Color.RED);
	}
	public void actionPerformed(ActionEvent e) 
	{
		int cnt = 0;
		String actionCommand = e.getActionCommand();
		if(actionCommand.equals("+")||actionCommand.equals("-")||actionCommand.equals("*") ||actionCommand.equals("/"))
			input +=" "+actionCommand+" ";//设置输入，把输入的样式改成 需要的样子
		else if(actionCommand.equals("C"))
			input = "";
		else if(actionCommand.equals("="))//当监听到等号时，则处理 input
		{
			input+= "="+compute(input);
			textField.setText(input);
			input="";
			cnt = 1;
		}
		else
			input += actionCommand;//数字为了避免多位数的输入 不需要加空格
		if(cnt==0)
		textField.setText(input);
	}
	private String compute(String input)//即1237 的 样例
	{
		String str[];
		str = input.split(" ");
		Stack s = new Stack();
		double m = Double.parseDouble(str[0]);
		s.push(m);
		for(int i=1;i