public void calculate(){
		char[]arr=input.getText().toCharArray();//將輸入的計算表達(dá)式字符串存儲在字符數(shù)組中便于查找運(yùn)算符的位置
		int i=0;//移動標(biāo)志變量
		while('0'<=arr[i]&&arr[i]<='9'||arr[i]=='.')//去除數(shù)字與小數(shù)點以確定雙目運(yùn)算符的位置
		      i++;
		char operator=arr[i];//將該運(yùn)算符存儲起來
		//雙目運(yùn)算
		if(operator!='%'&&operator!='√'){
			String s=input.getText(),s1,s2;//s1,s2分別存儲運(yùn)算符前后的數(shù)值字符串
			s1=s.substring(0,i);
			s2=s.substring(i+1,s.length());
			Double left=Double.parseDouble(s1);//將運(yùn)算符左邊的數(shù)值字符串轉(zhuǎn)換為浮點數(shù)
			Double right=Double.parseDouble(s2);//將運(yùn)算符右邊的數(shù)值字符串轉(zhuǎn)換為浮點數(shù)
			//根據(jù)不同的運(yùn)算符進(jìn)行相應(yīng)的計算
			if(operator=='+')result=left+right;
			else if(operator=='-')result=left-right;
			else if(operator=='×')result=left*right;
			else if(operator=='÷')result=left/right;
		}
		//單目運(yùn)算
		else{
			String s=input.getText(),s1;
			s1=s.substring(0,s.length()-1);
			Double a=Double.parseDouble(s1);
			if(operator=='%'){
				result=0.01*a;
			}
			else if(operator=='√'){
				result=Math.sqrt(a);
			}
		}
	}

            String str=input.getText();
			if(str.length()>1){
				str=str.substring(0,str.length()-1);
				input.setText(str);
			}
			else{
				input.setText("");
			}

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.StringTokenizer;
public class Calculator extends JFrame implements ActionListener{
	JTextField input;//文本框，顯示計算結(jié)果
	JButton []button=new JButton[20];//按鈕數(shù)組，存放20個按鈕組件
	JPanel pan=new JPanel();
	String name[]={"C","÷", "×", "←","7", "8", "9", "-", "4", "5", "6", "+", "1", "2", "3", "√", "%", "0", ".", "="};//按鈕標(biāo)簽數(shù)組
	double result;//存儲雙目運(yùn)算的結(jié)果
	public Calculator(){
		setTitle("模擬計算器—江海大");
		pan.setLayout(new GridLayout(5,4));//設(shè)置面板pan的布局格式為5行4列的網(wǎng)格布局，存放20個按鈕
		input=new JTextField(20);
		input.setText("");
		input.setFont(new Font("宋體",Font.BOLD,18));
		input.setForeground(Color.BLUE);
		for(int i=0;i<button.length;i++){
			button[i]=new JButton(name[i]);
			button[i].setFont(new Font("黑體",Font.BOLD,20));
			button[i].addActionListener(this);//給每一個按鈕注冊事件監(jiān)聽器
			pan.add(button[i]);
		}
		add(input,BorderLayout.NORTH);
		add(pan,BorderLayout.CENTER);
		setSize(600,400);
		setVisible(true);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//關(guān)閉窗體
	}
	//動作響應(yīng)
	public void actionPerformed(ActionEvent e){
		//如果點擊按鈕 "C"則觸發(fā)清空文本框的操作
		if(e.getSource()==button[0]){
			input.setText("");
		}
		//如果點擊按鈕"="則調(diào)用計算方法并在文本框顯示結(jié)果
		else if(e.getSource()==button[19]){
			calculate();
			input.setText(""+result);//輸出計算結(jié)果
		}
		//如果點擊"<--"按鈕則刪去文本框內(nèi)字符串的末尾字符
		else if(e.getSource()==button[3]){
			String str=input.getText();
			if(str.length()>1){
				str=str.substring(0,str.length()-1);
				input.setText(str);
			}
			else{
				input.setText("");
			}
		}
		//以字符串拼接的方式將點擊的按鈕的標(biāo)簽拼接起來，成為一個運(yùn)算表達(dá)式字符串
		else{
			input.setText(input.getText()+e.getActionCommand());
		}
	}
	public void calculate(){
		char[]arr=input.getText().toCharArray();//將輸入的計算表達(dá)式字符串存儲在字符數(shù)組中便于查找運(yùn)算符的位置
		int i=0;//移動標(biāo)志變量
		while('0'<=arr[i]&&arr[i]<='9'||arr[i]=='.')//去除數(shù)字與小數(shù)點以確定雙目運(yùn)算符的位置
		      i++;
		char operator=arr[i];//將該運(yùn)算符存儲起來
		//雙目運(yùn)算
		if(operator!='%'&&operator!='√'){
			String s=input.getText(),s1,s2;//s1,s2分別存儲運(yùn)算符前后的數(shù)值字符串
			s1=s.substring(0,i);
			s2=s.substring(i+1,s.length());
			Double left=Double.parseDouble(s1);//將運(yùn)算符左邊的數(shù)值字符串轉(zhuǎn)換為浮點數(shù)
			Double right=Double.parseDouble(s2);//將運(yùn)算符右邊的數(shù)值字符串轉(zhuǎn)換為浮點數(shù)
			//根據(jù)不同的運(yùn)算符進(jìn)行相應(yīng)的計算
			if(operator=='+')result=left+right;
			else if(operator=='-')result=left-right;
			else if(operator=='×')result=left*right;
			else if(operator=='÷')result=left/right;
		}
		//單目運(yùn)算
		else{
			String s=input.getText(),s1;
			s1=s.substring(0,s.length()-1);
			Double a=Double.parseDouble(s1);
			if(operator=='%'){
				result=0.01*a;
			}
			else if(operator=='√'){
				result=Math.sqrt(a);
			}
 
		}
	}
	public static void main(String[]args){
		new Calculator();
	}
}