Question

我有这个

abstract class Operand {
    public abstract <T extends Operand> Operand operation(Operator operator, T operand);
}
abstract class Numeric extends Operand {
}
class Integer extends Numeric 
    @Override
    public <Integer> Operand operation(Operator operator, Integer operand) {//problem
    }
}

我该如何解决这种情况？我不想在类操作数中使用泛型（因此我有操作数）因为我需要操作数是单一类型。在Integer的方法中我需要调用构造函数（new Integer（arg）），解决方案可能是以其他方式调用该方法。溶液

Answer 1

尝试重载方法

abstract class Operand {
    public abstract <T extends Operand> Operand operation(Operator operator, T operand);
}

abstract class Numeric<T extends Numeric<T>> extends Operand {
    public abstract Operand operation(Operator operator, T operand);
}

class Integer extends Numeric<Integer> {

    @Override
    public Operand operation(Operator operator, Integer operand) {
        // add your Integer specific code here
        return null; // replace null with actual returned value
    }

    @Override
    public <T extends Operand> Operand operation(Operator operator, T operand) {
        // simply call to overridden Integer specific method
        // no harm to downcast it here
        return operation(operator, (Integer) operand); 
    }

}

Answer 2

问题是您在Operand中的方法声明，即<T extends Operand>，您必须匹配＆＃34;合同＆＃34;与您的实施 -

class Integer extends Numeric {
  @Override
  public <T extends Operand> Operand operation(Operator operator, T operand) {
    // Like this....
  }
}

Answer 3

在我看来，你想要这样的东西：

abstract class Operand<T, U> {
    public abstract T operation(Operator operator, U operand);
}
abstract class Numeric<T, U> extends Operand<T, U> {
}
class Integer extends Numeric<Integer, Integer>
    @Override
    public Integer operation(Operator operator, Integer operand) {
    }
}

JAVA：类型参数隐藏类类型

3 个答案: