java - 如何用泛型参数覆盖具有对象参数的方法？

Question

我想重写具有 Object 类型参数的方法:

public void setValue(Object value) {
    // ...
}

并使该参数具有泛型类型T:

@Override
public void setValue(T value) {
    super.setValue(value);
}

如何在 Java 中执行此操作？

在 Eclipse 中我收到以下错误:

Multiple markers at this line
- The type parameter T is hiding the type T
- Name clash: The method setValue(T) of type TextField<T> has the 
 same erasure as setValue(Object) of type JFormattedTextField but does not 
 override it
- The method setValue(T) of type TextField<T> must override or 
 implement a supertype method

Answer 1

您不能使重写方法接受比它所重写的方法更窄的类型。

如果可以的话，以下是可能的:

class A {
    public setValue(Object o) {…}
}

class B<T> extends A {
    @Override
    public setValue(T o) {…};
}

A a = new B<String>(); // this is valid
a.setValue(new Integer(123)); // this line would compile, but make no sense at runtime