Java 泛型 T 与对象 [英] Java generics T vs Object

问题描述

我想知道以下两个方法声明有什么区别:

I was wondering what is the difference between the following two method declarations:

public Object doSomething(Object obj) {....}

public <T> T doSomething(T t) {....}

有什么你可以/愿意用一个而不是另一个做的吗?我在本网站的其他地方找不到这个问题.

Is there something you can/would do with one but not the other? I could not find this question elsewhere on this site.

推荐答案

与上下文隔离 - 没有区别.在 t 和 obj 上你只能调用 Object 的方法.

Isolated from context - no difference. On both t and obj you can invoke only the methods of Object.

但是有上下文 - 如果你有一个泛型类:

But with context - if you have a generic class:

MyClass<Foo> my = new MyClass<Foo>();
Foo foo = new Foo();

那么:

Foo newFoo = my.doSomething(foo);

与对象相同的代码

Foo newFoo = (Foo) my.doSomething(foo);

两大优势:

• 不需要强制转换(编译器对你隐藏了这个)
• 编译时安全有效.如果使用 Object 版本，您将无法确定该方法总是返回 Foo.如果它返回 Bar，您将在运行时遇到 ClassCastException.

• no need of casting (the compiler hides this from you)
• compile time safety that works. If the Object version is used, you won't be sure that the method always returns Foo. If it returns Bar, you'll have a ClassCastException, at runtime.

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