未初始化的原始实例变量是否使用内存？ [英] Do uninitialized primitive instance variables use memory?

问题描述

在Java中，在没有初始化的情况下声明类级实例变量会花费内存吗？

例如： int i; 使用任何内存，如果我没有用 i = 5; 初始化它？

In Java, does it cost memory to declare a class level instance variable without initializing it?
For example: Does int i; use any memory if I don't initialize it with i = 5;?

详细信息：

我有一个巨大的超级类，许多不同的（不同的，有自己的超级类）子类扩展。有些子类不使用超类声明的每个原语。我可以简单地将这些原语保留为未初始化，并仅在必要的子类中初始化它们以节省内存吗？

I have a huge super-class that many different (not different enough to have their own super classes) sub-classes extend. Some sub-classes don't use every single primitive declared by the super-class. Can I simply keep such primitives as uninitialized and only initialize them in necessary sub-classes to save memory?

推荐答案

类中定义的所有成员都有默认值，即使你没有明确地初始化它们，所以它们确实使用了内存。

All members defined in your classes have default values, even if you don't initialize them explicitly, so they do use memory.

例如，每个 int 默认初始化为 0 ，并将占用 4 字节。

For example, every int will be initialized by default to 0, and will occupy 4 bytes.

对于班级成员：

int i;

与以下内容相同：

int i = 0;

以下是JLS 说实例变量：

如果类T的字段a是实例变量，则创建新的实例变量a并将其初始化为默认值 （§4.12.5）作为每个新创建的T类对象或任何类的对象的一部分是T（第8.1.4节）的子类。在完成对象（第12.6节）的任何必要的最终化之后，当实例变量不再被引用时，实例变量实际上不再存在。

If a class T has a field a that is an instance variable, then a new instance variable a is created and initialized to a default value (§4.12.5) as part of each newly created object of class T or of any class that is a subclass of T (§8.1.4). The instance variable effectively ceases to exist when the object of which it is a field is no longer referenced, after any necessary finalization of the object (§12.6) has been completed.

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