JVM学习笔记-类（静态）变量(Class Variables)

 

Class variables are shared among all instances of a class and can be accessed even in the absence of any instance. These variables are associated with the class--not with instances of the class--so they are logically part of the class data in the method area. Before a Java Virtual Machine uses a class, it must allocate memory from the method area for each non-final class variable declared in the class.

类变量是由所有类实例共享的，但是即使没有任何类实例，它也可以被访问。这些变量只与类有关——而非类的实例，因此它们总是作为类型信息的一部分而存储在方法区。除了在类中生命的编译时常量外，虚拟机在使用某个类之前，必须在方法区中为这些类分配空间。

 

Constants (class variables declared final) are not treated in the same way as non-final class variables. Every type that uses a final class variable gets a copy of the constant value in its own constant pool. As part of the constant pool, final class variables are stored in the method area--just like non-final class variables. But whereas non-final class variables are stored as part of the data for the type that declares them, final class variables are stored as part of the data for any type that uses them. This special treatment of constants is explained in more detail in Chapter 6, "The Java Class File."

而编译时常量（就是那些用final声明以及用编译时已知的值初始化的类变量）则和一般的类变量的处理方式不同，每个使用编译时常量的类型都会复制它的所有常量到自己的常量池中，或嵌入到它的字节码流中。作为常量池或字节码流的一部分，编译时常量保存在方法区中——就和一般的类变量一样。但是当一般的类变量作为声明它们的类型的一部分数据而保存的时候，编译时常量作为使用它们的类型的一部分而保存。