泛型和铸造到正确的类型

Question

我的问题可以通过这个片段总结出来:

public interface TheClass<T> {
    public void theMethod(T obj);
}

public class A {
    private TheClass<?> instance;

    public A(TheClass<?> instance) {
        this.instance = instance;
    }

    public void doWork(Object target) {
        instance.theMethod(target); // Won't compile!

        // However, I know that the target can be passed to the
        // method safely because its type matches.
    }
}

我的类A使用TheClass其泛型类型未知的实例.它具有传递目标的方法,Object因为TheClass实例可以使用任何类进行参数化.但是,编译器不允许我像这样传递目标,这是正常的.

我该怎么做才能绕过这个问题？

一个肮脏的解决方案是将实例声明为TheClass<? super Object>,它工作正常但在语义错误...

我之前使用的另一个解决方案是将实例声明为原始类型TheClass,但这是不好的做法,所以我想纠正我的错误.

解

public class A {
    private TheClass<Object> instance; // type enforced here

    public A(TheClass<?> instance) {
        this.instance = (TheClass<Object>) instance; // cast works fine
    }

    public void doWork(Object target) {
        instance.theMethod(target); 
    }
}

Answer 1

public class A {
    private TheClass<Object> instance;

    public A(TheClass<Object> instance) {
        this.instance = instance;
    }

    public void do(Object target) {
        instance.theMethod(target); 
    }
}

或者

public class A<T> {
    private TheClass<T> instance;

    public A(TheClass<T> instance) {
        this.instance = instance;
    }

    public void do(T target) {
        instance.theMethod(target);
    }
}