在java中，内部类是否可以从内部类外部类之外定义的抽象类继承？

Question

In java can inner classes inherit from an abstract class defined outside of the inner class's outer class?

Also can abstract classes implement constructors?

Answer 1

Yes to both.

For example it is quite common to extend Swing Listener Adapter classes in inner classes

Why didn't you just try it?

Answer 2

Do you mean...

abstract public class Outer { 
 public Outer() { System.out.println("Outer.ctor"); }
 abstract public String foo(); 
}

public class Inner {
  public static class Inner2 extends Outer {
    public Inner2() { super(); }
    public String foo() { return "Inner2.foo";}
  }

  public static void main(String[] args) {
    System.out.println("main: " + new Inner2().foo());
  }
}

...?

$ javac -d .  Outer.java Inner.java

$ java -cp . Inner
Outer.ctor
main: Inner2.foo

(The superfluous calls to "super()" are merely illustrative, & are not necessary.)