4-例子1
 class Xiyoujipeople
  {   float hight,weight;
      String head, ear,hand,foot, mouth;
   void speak(String s)
 { 
      System.out.println(s);
 }
  }
class A
{  public static void main(String args[])
    {
    Xiyoujipeople zhubajie;//聲明對象。
    zhubajie=new  Xiyoujipeople();//為對象分配內存，使用 new和默認構造方法。
    …  … …. ….
        }
    }


4-例子2
class Point
{ 
     int x,y;
     Point()
      { x=12;y=16;
      }
     Point(int a,int b)
     {  x=a;y=b;
     }
 }
public class A
{ 
   public static void main(String args[])
{
 Point p1,p2;           //聲明對象p1和p2。
 p1=new Point();         //為對象分配內存，使用 new 和類中
     p2=new Point(23,35);     //的構造方法。
     …  …   …
 }
}


4-例子3
import java.applet.*;
import java.awt.*;
class Student
{ float math,english,sum;
   float f(float k1,float k2)
   {
     sum=k1*math+k2*english;
     return sum;
   } 
}
public class Average extends Applet
{ Student wanghong,lihong;
   public void init()
  { wanghong=new Student();
    lihong  =new Student();
    wanghong.math=60.0f;wanghong.english=80f;
    lihong.math=70.0f;  lihong.english=90.0f;
    wanghong.sum=wanghong.f(2.0f,2.0f);
    lihong.sum=lihong.f(2.0f,2.0f); 
  }
   public void paint(Graphics g)
  { g.drawString("lihong sum= "+lihong.sum,12,45);
    g.drawString("wanghong sum="+wanghong.sum,12,60);
  }
}  



4-例子4
import java.applet.*;import java.awt.*;
class Xiyoujipeople 
{ float height,weight;  String head,foot,hand,mouth;
  String speak(String s)
{ return s;
}
 }
public class Example4_4 extends Applet
{ Xiyoujipeople sunwukong,zhubajie;
  String s1,s2;
  public void init()
  { sunwukong=new Xiyoujipeople();
    zhubajie =new Xiyoujipeople();
zhubajie.weight=200f ;zhubajie.height=1.70f;
zhubajie.head="大頭";zhubajie.mouth="大嘴";
zhubajie.foot="兩只腳";zhubajie.hand="黑手";
sunwukong.weight=10000.0f ;sunwukong.height=1.60f;
sunwukong.head="一頭繡發";sunwukong.mouth="櫻桃小口";
sunwukong.foot="兩只小腳";sunwukong.hand="白嫩小手";
s1="我是豬八戒，做夢想娶媳婦"; s2="我是悟空，想騙豬八戒背我";   
  }
 public void paint(Graphics g)
 { g.setColor(Color.red);
   g.drawString(zhubajie.head+zhubajie.mouth+zhubajie.hand
                  +zhubajie.foot+zhubajie.hand,5,10);
 g.drawString("重量"+zhubajie.weight+"高"+zhubajie.height,5,30);
g.drawString(zhubajie.speak(s1),5,50);
g.setColor(Color.green);
g.drawString(sunwukong.head+sunwukong.mouth+sunwukong.hand
             +sunwukong.foot+sunwukong.hand,5,70);
g.drawString(sunwukong.speak(s2),5,90);
g.drawString("嘿嘿老孫重: "+sunwukong.weight,5,110); 
  }  
}



4-例子5
import java.applet.*;
import java.awt.*;
class Family
{ static String familyname;
         String name; 
  int age;     
}
public class Example4_5 extends Applet
{  Family father,son1,son2;
   public void init()
   { father=new Family();
     son1=new Family();
     son2=new Family();
     father.familyname="打";  father.name="鬼子";
     son1.name="漢奸";        son2.name="惡霸";
   }
   public void paint(Graphics g)
   { g.drawString("father: "+father.familyname+father.name,5,10);
     g.drawString("son1: "+son1.familyname+son1.name,5,20);
     g.drawString("son2: "+son2.familyname+son2.name,5,30);
     father.familyname="殺";
     g.drawString("father:"+father.familyname+father.name,5,40);
     g.drawString("son1: "+son1.familyname+son1.name,5,50);
     g.drawString("son2: "+son2.familyname+son2.name,5,65);
   }
}


4-例子6.
 import java.applet.*;
import java.awt.*;
class Father
{ private int money;
  float weight,height;
  String head;
  String speak(String s)
  { return s ;
  }
}
class Son extends Father
{ String hand ,foot;
} 
public class Example4_6 extends Applet
{ Son boy;
  public void init()
  { boy=new Son();
    boy.weight=1.80f;boy.height=120f;
    boy.head="一個頭";boy.hand="兩只手 ";boy.foot="兩只腳";
  }
  public void paint(Graphics g)
  { g.drawString(boy.speak("我是兒子"),5,20);
    g.drawString(boy.hand+boy.foot+boy.head+boy.weight+boy.height,5,40);
  }
}    



4-例子7
import java.applet.*;
import java.awt.*;
class Chengji
{ 
  float f(float x,float y)
  { return x*y;
  }
}
class Xiangjia  extends Chengji
{ float f(float x,float y)
  { return x+y ;
  }
}
public class Example4_7 extends Applet  
{ Xiangjia sum;
  public void init()
  { sum=new Xiangjia();
  }
  public void paint(Graphics g)
  { g.drawString("sum="+sum.f(4,6),5,20);
  }
}      



4-例子8
import java.applet.*;
import java.awt.*;
class Area
{ 
  float f(float r )
  { return 3.14159f*r*r;}
  float g(float x,float y)
  {return x+y;}
}
class Circle extends Area
{   float f(float r)
  {return 3.14159f*2.0f*r;}  
}
public class Example4_8 extends Applet
{ Circle yuan;
  public void init()
  { yuan=new Circle();
  } 
 public void paint(Graphics g)
  { g.drawString("yuan= "+yuan.f(5.0f),5,20);  //調用子類的方法f。
    g.drawString(" "+yuan.g(2.0f,8.0f),5,40);  //調用父類的方法g。
  }
}  



4-例子9
class Student 
 { int number;String name;
    Student(int number,String name)
    {this.number=number;this.name=name;
      System.out.println("I am "+name+ "my number is "+number);
    }
 }

class Univer_Student extends Student
 { boolean 婚否;
   Univer_Student(int number,String name,boolean b)
   { super(number,name);
     婚否=b;
     System.out.println("婚否="+婚否);
   }
 }
public class Example4_9
{public static void main(String args[])
 {Univer_Student zhang=new Univer_Student(9901,"和曉林",false);
 }
}

運行結果：
I am 和曉林 my number is 9901
婚否=false。




4-例子10
class Sum
 { int n;
  float f()
   { float sum=0;
     for(int i=1;i<=n;i++)
     sum=sum+i;
     return sum;  
   }
 }
class Average extends Sum 
 {   
   int n;  
   float f()
   {  float c;
      super.n=n;
      c=super.f();
      return c/n; 
   }
  float g()
   {float c;
    c=super.f();
    return c/2; 
   }
 }
public class Example4_10
{public static void main(String args[])
 {Average aver=new Average();
   aver.n=100;
   float result_1=aver.f();
   float result_2=aver.g();
   System.out.println("result_1="+result_1);
   System.out.println("result_2="+result_2);
 }
}

運行結果:
result_1=50.50
result_2=2525.0




4-例子11
import java.applet.*;import java.awt.*;
interface Computable
{ final int MAX=100;
  void speak(String s);
  int f(int x);
  float g(float x,float y);
}
class China implements Computable
{ int xuehao;
 public  int f(int x)         //不要忘記public關鍵字。
  {  int sum=0;
     for(int i=1;i<=x;i++)
      { sum=sum+i;}     return sum;
  }
 public float g(float x,float y)
  { return 6;   }                //至少有return語句。  
 public void speak(String s)
 { }
}
class Japan implements Computable
{ int xuehao;
 public int f(int x)
  { return 68; }
 public  float g(float x,float y)
  { return x+y;}
 public void speak(String s)
 { }                            //必須有方法體，但體內可以沒有任何語句。
}
public class Example4_9 extends Applet
{ China Li; Japan Henlu;
  public void init()
  { Li=new China();Henlu=new Japan(); Li.xuehao=991898;Henlu.xuehao=941448;
  }
  public void paint(Graphics g)
  { g.drawString("xuehao:"+Li.MAX+Li.xuehao+"從1到100求和"+Li.f(100),10,20);
g.drawString("xuehao:"+Henlu.MAX+Henlu.xuehao+"加法"+Henlu.g(2.0f,3.0f),10,40);
  }
}