非初始化和初始化为null之间有什么区别？ [英] What's the difference between non-initialisation and initialising to null?

问题描述

我有这段代码：

MyClass object;

.... some code here where object may or may not be initialised...

if (object.getId > 0) {
    ....
}

导致编译错误： object 可能尚未初始化，这是公平的。

Which results in a compile error: object may not have been initialised, which is fair enough.

现在我将我的代码更改为：

Now I change my code to this:

MyClass object;

.... some conditional code here where object may or may not be initialised...

if (object != null && object.getId > 0) {
     ....
}

我得到相同的编译错误！我必须将 object 初始化为null：

I get the same compile error! I have to initialise object to null:

MyClass object = null;

那么不初始化对象和初始化为null之间的区别是什么？如果我声明一个没有初始化的对象，那么它不是null吗？

So what's the difference between not initialising an object, and initialising to null? If I declare an object without initialisation isn't it null anyway?

谢谢

推荐答案

• 字段（成员变量）初始化为 null （或默认原始值，如果它们是基元）


• 本地变量未初始化，您负责设置初始值。


• fields (member-variables) are initialized to null (or to a default primitive value, if they are primitives)
• local variables are not initialized and you are responsible for setting the initial value.

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