calculatordemo.java

本java源程序包括了大量的学习程序（共27章）方便大家学习

import java.awt.*;
import java.applet.*;
public class CalculatorDemo extends Applet
{
    TextField answerText; 
    //显示输入和结果的文本域
  	Button pointButton,equalButton,plusButton,minusButton,clearButton,multiButton,divisionButton; 
  	//运算符按钮
	Button[] b=new Button[10];  //数字按钮
  
  	String currentOp,preOp; //当前操作和上一步操作
	String foreText,backText; //当前输入和上一次输入
  	boolean isFloat = false; //运算类型标志
  	public void init() 
  	{
  		//实例化面板
	  	Panel panel1=new Panel();  //实例化面板
		Panel panel2=new Panel();
		Panel panel3=new Panel();	
	    currentOp = new String(""); 
	    //实例化各组件
	    preOp = new String("");
	    foreText = new String("");
	    backText = new String("");
	    answerText = new TextField(8);
	    setBackground(Color.lightGray);   //设置Applet背景色
	    setForeground(Color.blue);        //设置Applet前景色  	    
		for(int i=9;i>=0;i--)
		{ 
			b[i]=new Button(Integer.toString(i)); 
			//实例化数字按钮
			panel2.add(b[i]); //增加按钮到面板
		}        
	 
	    pointButton = new Button("."); //实例化按钮
	    equalButton = new Button("=");
	    equalButton.setForeground(Color.red);   //设置按钮前景色
	    clearButton = new Button("清除");
	    clearButton.setForeground(Color.red);
	    divisionButton = new Button("/");
	    divisionButton.setForeground(Color.red);
	    multiButton = new Button("*");
	    multiButton.setForeground(Color.red);
	    minusButton = new Button("-");
	    minusButton.setForeground(Color.red);    
	    plusButton = new Button("+");
	    plusButton.setForeground(Color.red);    
		setLayout(new FlowLayout()); //设置布局管理器
		panel1.setLayout(new FlowLayout());
		panel2.setLayout(new GridLayout(4,3));
		panel3.setLayout(new GridLayout(4,1));
	    panel1.add(answerText); //增加组件到面板
		panel1.add(clearButton);
		panel2.add(pointButton);
		panel2.add(equalButton);
		panel3.add(plusButton);
		panel3.add(minusButton);
		panel3.add(multiButton);
		panel3.add(divisionButton);
		add(panel1); //增加组件到Applet
		add(panel2);
		add(panel3);	
  	}
  
  	public boolean action(Event e, Object o) 
  	{ //事件处理
    	String s = new String("");
     	for(int i=0;i<10;i++){
			if(e.target==b[i]||e.target==pointButton)
			{ //按钮事件来自于数字按钮和点按钮
        		if(e.target != pointButton) 
        		{
          			s = (String)o;
          			doForeText(s); //处理输入
        		}
        		if((e.target == pointButton)&&(!isFloat))
        		{ //浮点数输入
          			isFloat = true; //设置运算标志
         			s = (String)o;
          			if(foreText.equals(""))
          			{
           	 			foreText += "0.";  //增加小数点前面0
          			}
          			else
          			{
            			doForeText(s);
          			}
        		}
      		}
      	}      
      	if(e.target == clearButton) 
      	{
        	doClear();  //清除输入
      	}      
      	if((e.target == multiButton)||(e.target == divisionButton)
      	    ||(e.target == plusButton)||(e.target == minusButton)) 
      	{ //处理运算
        	if(foreText != "")
        	{
         		currentOp = ((String)o);
          		doOperator();  //处理运算
        	}
        	else 
        	{
          		preOp = ((String)o);
          	}
      	}      
      	if(e.target == equalButton) 
      	{ //等于按钮事件处理
        	doOperator(); //处理运算
      	}  
		return true;  
	}
  	public void doOperator()
  	{
    	double dFore,dBack;
    	Double d;
    	if(preOp.equals("")) 
    	{
      		backText = foreText;
      		foreText = "";
      		answerText.setText(backText); //显示文本
    	}
    	else 
    	{
      		dFore = (new Double(foreText)).doubleValue(); //得到第一输入
      		dBack = (new Double(backText)).doubleValue(); //得到第二输入
      		foreText = "";
      		backText = answerText.getText(); 
      
	      	if(preOp.equals("+")) 
	      	{ //加运算处理
	        	d = new Double((dBack + dFore)); //得到运算结果
	        	answerText.setText(d.toString());  //显示运算结果
	        	backText = d.toString();
	      	}
	      	if(preOp.equals("-")) 
	      	{
	        	d = new Double((dBack - dFore));//得到运算结果
	        	answerText.setText(d.toString()); //显示运算结果
	        	backText = d.toString();
	      	}
	      	if(preOp.equals("*")) 
	      	{
	        	d = new Double((dBack * dFore));//得到运算结果
	        	answerText.setText(d.toString());//显示运算结果
	        	backText = d.toString();
	      	}
	      	if(preOp.equals("/")) 
	      	{
	      		if (dFore==0)
	      		{
	      			answerText.setText("除数不能为0"); //显示出错信息
	      			return;
	      		}
	       		d = new Double((dBack / dFore));//得到运算结果
	        	answerText.setText(d.toString());//显示运算结果
	        	backText = d.toString();
	      	}
    	}
    	preOp = currentOp;
  	}
  	public void doForeText(String s) 
  	{
    	foreText += s;
    	answerText.setText(foreText); //显示输入
  	}
  
  	public void doBackText(String s)
  	{
    	backText = foreText;
    	foreText = "";
    	answerText.setText(foreText); //显示输入
  	}
 	public void doClear() { //清除输入
    	currentOp = "";
    	preOp = "";
    	foreText = "";
    	backText = "";
    	isFloat = false;
    	answerText.setText(""); 
  	}
}