引用内部类的封闭实例 [英] Referencing an enclosing instance from an inner class

问题描述

这只是一个知识/好奇心问题。

在Java工作了几年之后，这只是让我感到震惊。

  class Foo {
 
 class Bar {
 
 Foo.this.doSomething（）; 
 
} 
 
} 
  

当我看在 Foo.this ，我认为它是一个静态参考，显然不是这种情况。

我知道这是Java规范的一部分，但确切地说当你使用< Class> .this ？

这是它只是的东西吗？

解决方案

< blockquote>

我知道这是Java规范的一部分，但确切地说当你使用.this时会发生什么？

它只是指 Bar 中的隐藏字段。通过反编译最容易看到这一点。你会看到有一个 Bar 构造函数，它引用了一个 Foo 的实例。该引用存储在一个字段中，然后当你使用 Foo.this 时，它只是访问该字段。假设您将 Foo.this.doSomething（）放入 someMethod 调用，您的代码类似于：

  class Foo {
 
 static class Bar {
 private final Foo $ foo; 
 
 Bar（Foo foo）{
 this。$ foo = foo; 
} 
 
 public void someMethod（）{
 $ foo.doSomething（）; 
} 
} 
} 
  

This is a knowledge/curiosity question only.

After several years in Java, this has only just struck me.

class Foo {

   class Bar{

      Foo.this.doSomething();

   }

}

When I look at Foo.this, I would assume that it's a static reference which obviously is not the case.

I know this is part of the Java spec, but exactly what is going on when you use <Class>.this?

Is it one of those "it just is" things?

解决方案

I know this is part of the Java spec, but exactly what is going on when you use .this?

It just refers to a "hidden" field within Bar. It's easiest to see this by decompiling. You'll see that there's a Bar constructor taking a reference to an instance of Foo. That reference is stored in a field, and then when you use Foo.this, it just accesses that field. So assuming you'd put your Foo.this.doSomething() into a someMethod call, your code is similar to:

class Foo {

   static class Bar {
      private final Foo $foo;

      Bar(Foo foo) {
          this.$foo = foo;
      }    

      public void someMethod() {
          $foo.doSomething();
      }
   }
}

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