练习作业

【上机作业】【java】2010.3.31 类的多态性

import java.text.DecimalFormat;

class math{

         public int plus(int a,int b){

         return a+b;

         }

         public String plus(double a,double b){

         DecimalFormat format=new DecimalFormat(“#.000”); 

         double oldDouble;

         oldDouble=a+b;

         String newDouble = format.format(oldDouble );

         return newDouble;

         }

         public int minus(int a,int b){

         return a-b;

         }

         public String minus(double a,double b){

         DecimalFormat format=new DecimalFormat(“#.000”); 

         double oldDouble;

         oldDouble=a-b;

         String newDouble = format.format(oldDouble );

         return newDouble;

         }

         public int multiply(int a,int b){

         return a*b;

         }

         public String multiply(double a,double b){

         DecimalFormat format=new DecimalFormat(“#.000”); 

         double oldDouble;

         oldDouble=a*b;

         String newDouble = format.format(oldDouble );

         return newDouble;

         }

         public int division(int a,int b){

         if(b==0){

                   System.out.println(“error!”);

                            return 0;

                   }

         else

         return a/b;

         }

         public String division(double a,double b){

         if(b==0){

                   System.out.println(“error!”);

                            return “0”;

                   }

         else{

         DecimalFormat format=new DecimalFormat(“#0.000”); 

         double oldDouble;

         oldDouble=a/b;

         String newDouble = format.format(oldDouble );

         return newDouble;

         }

         }

public static void main(String []args){

         math m=new math();

         System.out.println(“1+2=”+m.plus(1,2));

         System.out.println(“1-2=”+m.minus(1,2));

         System.out.println(“1*2=”+m.multiply(1,2));

         System.out.println(“1/2=”+m.division(1,2));

         System.out.println(“——————————————–“);

         System.out.println(“1.1+2.2=”+m.plus(1.1,2.2));

         System.out.println(“1.1-2.2=”+m.minus(1.1,2.2));

         System.out.println(“1.1*2.2=”+m.multiply(1.1,2.2));

         System.out.println(“1.1/2.2=”+m.division(1.1,2.2));

         }

}

class Animal{

         String name,color;

         double weight;

         public Animal(String n,String c,double w){

         name=n;

         color=c;

         weight=w;

         }

         void speak(){

         System.out.println(“I’m “+name); 

         }

         void eat(){

         }

}

class Dog extends Animal{

         public Dog(String n,String c,double w){

         super(n,c,w);

         }

         void speak(){

         System.out.println(“wang wang”);

         }

         void eat(){

         System.out.println(“eat bone”);     

         }

}

class Rabbit extends Animal{

         public Rabbit(String n,String c,double w){

         super(n,c,w);

         }

         void speak(){

         System.out.println(“aaaaaaaaaa”);       

         }

         void eat(){

         System.out.println(“eat grass”);    

         }

}

class display{

         public static void main(String []args){

         Dog d=new Dog(“Dog”,”yellow”,10.2);

         Rabbit r=new Rabbit(“Rabbit”,”black”,5.5);

         d.speak();

         d.eat();

         r.speak();

         r.eat();

         }

} 

class Animal{

         String name,color;

         double weight;

         public Animal(String n,String c,double w){

         name=n;

         color=c;

         weight=w;

         }

         void speak(){

         System.out.println(“I’m “+name); 

         }

         void eat(){

         }

}

class Dog extends Animal{

         public Dog(String n,String c,double w){

         super(n,c,w);

         }

         void speak(){

         System.out.println(“wang wang”);

         }

         void eat(){

         System.out.println(“eat bone”);     

         }

}

 

class Rabbit extends Animal{

         public Rabbit(String n,String c,double w){

         super(n,c,w);

         }

         void speak(){

         System.out.println(“aaaaaaaaaa”);       

         }

         void eat(){

         System.out.println(“eat grass”);    

         }

}

class display{

 

         public static void main(String []args){

         Dog d=new Dog(“Dog”,”yellow”,10.2);

         Rabbit r=new Rabbit(“Rabbit”,”black”,5.5);

 

         d.speak();

         d.eat();

         r.speak();

         r.eat();

         }

}

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