Question

我有这个界面：

public interface Numeric
{
    public Numeric addition(Numeric x,Numeric y);
    public Numeric subtraction(Numeric x,Numeric y);
}

这堂课

public class Complex implements Numeric
{
    private int real;
    private int img;

    public Complex(int real, int img){
        this.real = real;
        this.img = img;
    }

    public Numeric addition(Numeric x, Numeric y){
        if (x instanceof Complex && y instanceof Complex){
            Complex n1 = (Complex)x;
            Complex n2 = (Complex)y;

            return new Complex(n1.getReal() + n1.getReal(), n2.getImg() + 
            n2.getImg()); 

        } 
        throw new UnsupportedOperationException();
    }

    public Numeric subtraction(Numeric x, Numeric y){
        if (x instanceof Complex && y instanceof Complex){
            Complex n1 = (Complex)x;
            Complex n2 = (Complex)y;

            return new Complex(n1.getReal() - n1.getReal(), n2.getImg() - 
            n2.getImg()); 

        } 
        throw new UnsupportedOperationException();
    }

    public int getReal(){
        return real;
    }

    public int getImg(){
        return img;
    }
}

为什么会出现此错误：

不兼容的类型：数字不能转换为复杂的

当我运行这段代码时：

public class TestNumeric
{
    public static void main(String[] args){
        Complex c1 = new Complex(3, 4);
        Complex c2 = new Complex(1, 2);
        Complex rez;

        rez = rez.addition(c1, c2);
    }
}

错误在“ rez = rez.addition（c1，c2）;”行中
复合体实现数字，因此每个数字都是复合体，对吗？我已经在附加方法中进行了转换和检查。为什么会出现此错误，该如何解决？

Answer 1

addition和subtraction的声明是错误的。应该如下：

public interface Numeric {
    public Numeric addition(Numeric obj);

    public Numeric subtraction(Numeric obj);
}

，然后您对addition和subtraction的实现应如下：

public Numeric addition(Numeric obj){
    if (obj instanceof Complex){
        Complex n = (Complex)obj;

        return new Complex(this.getReal() + n.getReal(), this.getImg() + 
        n.getImg()); 
    } else {
        throw new UnsupportedOperationException();
    }
}

最后，TestNumeric应该如下：

public class TestNumeric {
    public static void main(String[] args) {
        Numeric c1 = new Complex(3, 4);
        Numeric c2 = new Complex(1, 2);
        Numeric rez = c1.addition(c2);
    }
}

更新：

@OrosTom-根据您的评论，我添加了需要放入类Complex中的方法，以便您可以打印结果

@Override
public String toString() {
    return real + " + " + img + "i";
}

此后，输出以下代码

public class TestNumeric {
    public static void main(String[] args) {
        Numeric c1 = new Complex(3, 4);
        Numeric c2 = new Complex(1, 2);
        Numeric rez = c1.addition(c2);
        System.out.println(c1);
        System.out.println(c2);
        System.out.println(rez);
    }
}

将是

3 + 4i
1 + 2i
4 + 6i

Java。为什么我不能将接口对象转换为类对象？

1 个答案: