类的继承和多态

1.设计一个抽象类，声明有关算术运算的方法，并创建四个子类继承该抽象的类，完成进行加、减、乘、除四则运算。

publicabstract  class  calculate {
      public abstract double A(double a,doubleb);
}
public class addextends calculate{
            public double A(double a,double b){
               return a+b;
            }
}
public class subextends calculate{
      public double A(double a,double b){
          return a-b;
       }
}
public class mulextends calculate {
      public double A(double a,double b){
          return a*b;
       }
}
public class divextends calculate{
      public double A(double a,double b){
           return a/b;
       }
}
public class Main {
      public static void main(String[] args) {
           add h1=new add();
           sub h2=new sub();
           mul h3=new mul();
           div h4=new div();
           System.out.println("1+2="+h1.A(1,2)+" 1-2="+h2.A(1, 2)+" 1*2="+h3.A(1, 2)+"1/2="+h4.A(1, 2));
      }
}

2.编写一个类，该类有如下一个方法：

public int f(inta,int b){……//要求该方法将返回a和b的最大公约数}，再编写一个该类的子类，要求子类重写方法f()，而且重写的方法将返回两个正整数的最小公倍数。

public class lcmextends gcd{
      public int f(int a,int b){
           gcd tem=new gcd();
           return a*b/tem.f(a, b);
      }
}
public class gcd {
      public int f(int a,int b){
           if(a<b){
                 int t=a;a=b;b=t;
           }
           while(a%b!=0){
                 int t=a%b;
                 a=b;b=t;
           }
           return b;
      }
}
public class Main {
      public static void main(String[] args) {
           gcd A=new gcd();
           lcm B=new lcm();
           System.out.println("14和21的最大公约数="+A.f(14, 21)+"\n14和21的最小公倍数="+B.f(14,21));
      }
}

3.编写一个圆锥类，能够计算圆锥的体积，要求圆锥类的构造函数中有一参数是圆类的一个对象。

public class yuanzhui {
	double v;
	yuanzhui(double r,double h)
	{
		yuan S=new yuan(r);
		v=S.s*h/3.0;
	}
	yuanzhui(){}
	void set(double r,double h)
	{
		yuan S=new yuan(r);
		v=S.s*h/3.0;
	}
}

public class yuan {
	double s;
	yuan(double r){
		s=3.14*r*r;
	}
	yuan(){}
	void set(double r)
	{
		s=3.14*r*r;
	}
}
public class Main {
	public static void main(String[] args) {
	yuanzhui a1=new yuanzhui(5,3);
	yuanzhui a2=new yuanzhui();
	a2.set(5,3);
	System.out.println("a1的体积="+a1.v+"  a2的体积="+a2.v);
	}
}

4.定义接口Shape，其中包括Area方法。类Circle、Square和Triangle均实现了接口Shape。定义主函数，创建元素个数为3的Shape类型的一维数组，分别为数组元素创建Circle、Square和Triangle类型的对象，最后分别调用各数组元素的Area方法，输出相关信息。

public interface Shape{
	double Area();
}
public class Circle implements Shape{
	double s;
	Circle(double r){
		s=r*r*3.14;
	}
	public double Area() {
		return s;
	}
}
public class Square implements Shape{
	double s;
	Square(double l){
		s=l*l;
	}
	public double Area() {
		return s;
	}
}
public class Triangle implements Shape{
	double s;
	Triangle(double l,double w){
		s=l*w/2.0;
	}
	public double Area() {
		return s;
	}
}
public class gbb {
	public static void main(String[] args) {
		Shape []a={ new Circle(2),new Square(4),new Triangle(3,3)};
		System.out.println("a[0]是圆，半径2，面积为："+a[0].Area()+"   a[1]是正方形，边长4，面积为："+a[1].Area()+"    a[2]是三角形，底长3，高为3，面积为："+a[2].Area());
	}
}