例5-8和例5-9和5-10

class A{
 double n;
 int m;
 void f(){
     System.out.printf("子类继承方法f(),n=%f,m=%d\n",n,m);
 }
 void g(){
     System.out.printf("你好，n=%f,m=%d\n",n,m);
 }
}
class B extends A{
 int n=12;
 void g(){
     System.out.printf("子类重写方法g(),n=%d,m=%d\n",n,m);
 }
 void cry(){
     System.out.printf("子类新增的方法,n=%d,m=%d\n",n,m);
 }
}
public class Example5_8{
 public static void main(String args[]){
  A a;
  a=new B();
  a.n=0.618;
  a.m=200;
  a.f();
  a.g();
  B b=(B)a;
  b.n=555;
  b.cry();
 }
}

class Animal{
     void cry(){}
}
class Dog extends Animal{
     void cry(){
         System.out.println("Wang!Wang!......");
     }
}
class Cat extends Animal{
     void cry(){
         System.out.println("Miao~~Miao~~...");
     }
}
public class Example5_9{
  public static void main(String args[]){
       Animal animal;
       animal=new Dog();
       animal.cry();
       animal=new Cat();
       animal.cry();
    }
 }
  

public abstract class Geometry{
  public abstract double getArea();
 }

public class Pillar{
 Geometry bottom;
 double height;
 Pillar(Geometry bottom,double height){
  this.bottom=bottom;
  this.height=height;
  }
  void changeBottom(Geometry bottom){
   this.bottom=botttom;
  }
  public double getVolume(){
   return bottom.getArea()*height;
  }
 }
 public class Lader extends Geometry{
    double a,b,h;
    Lader(double a,double b,double h){
      this.a=a;
      this.b=b;
      this.h=h;
  }
  public double getArea(){
   return((1/2.0)*(a+b)*h);
  }
 }
 public class Circle extends Geometry{
    double r;
    Circle(double r){
      this.r=r;
    }
    public double getArea(){
      return(3.14*r*r);
    }
  }
  
  public class Example5_10{
   public static void main(String args[]){
    Pillar pillar;
    Geometry tuxing;
    tuxing=new Lader(12,22,100);
    System.out.println("梯形的面积"+tuxing.getArea());
    Pillar=new Pillar(tuxing,58);
    System.out.println("梯形底的柱体的体积"+pillar.getVolume());
    tuxing=new Circle(10);
    System.out.println("半径是10的圆的面积"+tuxing.getArea());
    pillar.changeBottom(tuxing);
    System.out.println("圆形底的柱体的体积"+pillar.getVolume());
   }
  }