一、加法

import java.io.*;     //导入输入输出包
public class MyClass 
{
    private int val1,val2;

    public void myFun(int x,int y)
    {
        val1=x;
        val2=y;
        System.out.println("the sum is "+(val1+val2));
    }
    
    //主函数
    public static void main(String arg[])
    {
        MyClass MyObj=new MyClass();  //新建一个MyClass实类
        MyObj.myFun(3,4);  //调用求和函数myFun
    }
}

	
	

		
	

二、一个简单的Applet

import java.awt.Graphics;
import java.applet.Applet;
public class MyFirstJavaApplet extends Applet
{
        public String s;
        public void init()
        {     
             s=new String("Hello World !");
        }
        public void paint(Graphics g)
        {   
             g.drawString(s,25,25);  
        }
}

	
	

		
	

三、定义一个圆的类CCirle

class CCircle   {
  double pi;    
  double radius;
  double getRadius(){
   return radius;
}
  void setCircle(double r, double p){     
      pi=p;
      radius=r;   
   }
}
public class TestCCircle{
   public static void main(String args[])   {
      CCircle cir1=new CCircle();   
      cir1.setCircle(2.0,3.1416);
      System.out.println("radius="+cir1.getRadius()); 
   }
}

	
	

		
	

四、定义圆的面积函数

class CCircle   {
  double pi;    
  double radius;
  double getArea(){
    return radius*radius*pi;
}
  void setCircle(double r, double p){     
      pi=p;
      radius=r;   
   }
}
public class TestCCircleArea{
   public static void main(String args[])   {
      CCircle cir1=new CCircle();   
      cir1.setCircle(2.0,3.1416);
      System.out.println("area="+cir1.getArea()); 
   }
}

	
	

		
	

五、主方法在TestArea.java中，调用CCircle的方法，完成面积计算

public class TestArea{
   public static void main(String args[])   {
      CCircle cir1=new CCircle();   
      cir1.setCircle(2.0,3.1416);
      System.out.println("area="+cir1.getArea()); 
   }
}7

public class CCircle   {
  double pi;    
  double radius;
  double getArea(){
    return radius*radius*pi;
}
  void setCircle(double r, double p){     
      pi=p;
      radius=r;   
   }
}

	
	

		
	

六、将PI的值改为3.14159

class CCircle   {
  double pi;    
  double radius;
  double getArea(){
    return radius*radius*pi;
}
  void setCircle(double r, double p){     
      pi=p;
      radius=r;   
   }
}
public class TestPiArea{
   public static void main(String args[])   {
      CCircle cir1=new CCircle();   
      cir1.setCircle(2.0,3.14159);
      System.out.println("area="+cir1.getArea()); 
   }
}