Java最佳实践-内部类访问外部类的静态变量

Question

class OuterClass {
    static int j=99;

    static class InnerClass {

        public void doSomething() {
            while(true)
                OuterClass.j= 100;
            } 
        }
    } 
}   

Using the above code, is there any issue with garbage collection when the OuterClass needs to garbage collect but lets say doSomething is referencing a static variable will it be an issue ? What i'm concerned with is that the inner class has a reference to the outer class by accessing the variable j and im wondering if that will affect the OuterClass being GC.

Answer 1

Although you've named it InnerClass , it is not an inner class. It is simply a static nested class.

An instance of such a class has no reference to any instance of the enclosing class. What's more, you're referencing a static field of the enclosing class. There is absolutely no reference to any instance of OuterClass .

Nothing in your InnerClass can prevent an instance of the type OuterClass from being garbage collected.

_{Did I misunderstand your question? Are you asking about classes being garbage collected?}

Answer 2

Classes aren't affected by GC, objects are. If you create an object of type InnerClass, GC will not touch anything referred to by it. However, because you are only referencing a static variable, you are not referencing any objects of type OuterClass (in that code fragment anyway). Thus, GC is free to remove any unneeded objects of type OuterClass without affecting, in any way, the functioning of objects of type InnerClass.

Note that if all you're doing is referring to a static variable in OuterClass from your InnerClass, you should probably not define InnerClass as a nested class.

Answer 3

Since the j field is static, it exists beyond the scope of a single instance of OuterClass. The fact that InnerClass is static decouples it from any instance of OuterClass.

As with class methods and variables, a static nested class is associated with its outer class. And like static class methods, a static nested class cannot refer directly to instance variables or methods defined in its enclosing class: it can use them only through an object reference.

Note: A static nested class interacts with the instance members of its outer class (and other classes) just like any other top-level class. In effect, a static nested class is behaviorally a top-level class that has been nested in another top-level class for packaging convenience.

Nested classes explained in the Java tutorial