在java

Question

我有简单的用例，但至少对我来说似乎很棘手。

我有课

   public class Operation {
    private int a,b;
    public Operation(){

    }
    public Operation(int a,int b){

        this.a=a;
        this.b=b;       
    }
    public int calculate()
    {
        return (a+b);
    }

}

和四个扩展Operation

的类

public class Addition extends Operation {
    public Addition(){
        super();
    }
    public Addition(int a,int b){
        super(a,b);     
    }
    public int calculate(int a,int b)
    {

                return (a+b);
    }

}
public class Subtraction extends Operation {
    public Subtraction()
    {

    }
    public Subtraction(int a,int b)
    {
        super(a,b); 
    }
    public int calculate(int a,int b)
    {
        return (a-b);
    }

}
public class Multiplication extends Operation {
    public Multiplication()
    {

    }
    public Multiplication(int a,int b)
    {
        super(a,b); 
    }
    public int calculate(int a,int b)
    {
        return (a*b);
    }

}
public class Division extends Operation {
    public Division()
    {

    }
    public Division(int a,int b)
    {
        super(a,b); 
    }
    public int calculate(int a,int b)
    {
        return (a/b);
    }


}

我的Main方法必须遵循

public class CalculationTest {

    public static void main(String[] args) {
        Operation op=new Addition(100,200);
        System.out.println(op.calculate());
        op=new Subtraction();
        System.out.println(op.calculate()); //this should print -100 as output
        op=new Multiplication();
        System.out.println(op.calculate()); //this should print 2000 as output
        op=new Division();
        System.out.println(op.calculate()); //this should print 0 as output


    }

}

我必须得到输出 300 -100 2000 0 但我得到了输出 300 0 0 0

提前致谢

Answer 1

  

我必须得到输出300 -100 2000 0但我输出为300 0 0 0

那是因为你没有给他们任何意见。

Operation op=new Addition(100,200);

这有输入并且有效。

 op=new Subtraction();

这没有输入，因此值默认为0，结果为0.

如果你想减去两个值，你仍然需要提供它们，试试

 op = new Subtraction(100, 200);