java - java中外部类和内部类是如何关联的？

Question

我知道java中内部类的每个实例都与其外部类的一个实例相关联，但我想知道这个过程是如何进行的。

更具体地说，当你写下类似的内容时

public class Outer {
    Inner root;

    class Inner {
        public Inner() {
             next = (Math.random() > 0.5)? new Inner(): null;
        }

        Inner next;
    }
}

root、root.next 等...如何与同一个 Outer 实例关联？编译器是否向内部构造函数添加参数？

Answer 1

How are root, root.next, etc... all associated with the same instance of Outer?

Java Language Specification section on Determining Enclosing Instances在类实例创建期间状态:

Let C be the class being instantiated, and let i be the instance being created. If C is an inner class, then i may have an immediately enclosing instance (§8.1.3), determined as follows:

• [...]
• If C is an inner member class, then:
  • If the class instance creation expression is unqualified, then:

    • If the class instance creation expression occurs in a static context, then a compile-time error occurs.

    • Otherwise, if C is a member of a class enclosing the class in which the class instance creation expression appears, then let O be the immediately enclosing class of which C is a member. Let n be an integer such that O is the n'th lexically enclosing type declaration of the class in which the class instance creation expression appears.

      The immediately enclosing instance of i is the n'th lexically enclosing instance of this.

    • Otherwise, a compile-time error occurs.

换句话说，当你执行时

next = (Math.random() > 0.5)? new Inner(): null;

Inner正在实例化的类； Inner是包含该类的类的成员( Inner ，即其本身)​​，其中 new Inner()出现； Outer是 Inner 的直接封闭类;因为Inner是 Outer 的内部类，必须有一个 this那this保证有 Outer封闭实例；最后，该封闭实例成为 i 的封闭实例，新Inner正在创建实例。

简而言之，它重用了 Outer 的同一个实例。 。

Does the compiler add a parameter to the Inner constructor?

Java Language Specification section on the Formal Parameters of Constructors状态:

The constructor of a non-private inner member class implicitly declares, as the first formal parameter, a variable representing the immediately enclosing instance of the class (§15.9.2, §15.9.3).

所以，是的。