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

问题描述

我想知道以下两种方法声明有什么不同：

  public Object doSomething（Object obj）{。 ...} 
 
 public< T> T doSomething（T t）{...} 
  

您可以/可以做些什么一个而不是另一个？我在这个网站的其他地方找不到这个问题。 解决方案

在 t 和 obj 上，您只能调用 Object


但是有了上下文 - 如果你有一个泛型类：

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

然后：



  Foo newFoo = my.doSomething（foo）; 
  

与对象相同的代码



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

两个优点：$ b​​
$ b $ ul


不需要强制转换（编译器将此隐藏起来）

编译时间安全性可行。如果使用 Object 版本，您不能确定该方法总是返回 Foo 。如果它返回 Bar ，那么在运行时您将有一个 ClassCastException 。

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

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

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

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

解决方案

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

But with context - if you have a generic class:

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

Then:

Foo newFoo = my.doSomething(foo);

Same code with object

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

Two advantages:

• 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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