JAVA内部类要点及面试题

（编辑整理中...）

 

QUESTION NO: 4

1. public class Outer{

2. public void someOuterMethod() {

3. // Line 3

4. }

5. public class Inner{}

6. public static void main( String[]argv ) {

7. Outer o = new Outer();

8. // Line 8

9. }

10. }

Which instantiates an instance of Inner?

A. new Inner(); // At line 3

B. new Inner(); // At line 8

C. new o.Inner(); // At line 8

D. new Outer.Inner(); // At line 8//new Outer().new Inner()

答案如下：

publicclass Outer {

    publicvoid someOuterMethod() {

       // Line 3

       new Inner();//放在这里不出错

    }

    publicclass Inner {

    }

    publicstaticvoid main(String[] argv) {

       Outer o= new Outer();

       // Line 8

       //o不能够被解释成为一种类型，出错

       //new o.Inner();

       /**

        *下面两种用法，都报下面的错误：

        *NoenclosinginstanceoftypeOuterisaccessible.

        *Mustqualifytheallocationwithanenclosinginstance

        *oftypeOuter(e.g.x.newA()wherexisaninstanceofOuter)

        */   

       //new Outer.Inner();

       //new Inner();      

    }

}

 

以上ref:http://blog.csdn.net/fenglibing/article/details/1753536

 

1.关键字 .this与.new （ref:http://www.iteye.com/topic/442435）

public class Outer {private int num;public Outer() {}public Outer(int num) {this.num = num;}private class Inner {public Outer getOuter() {return Outer.this;}public Outer newOuter() {return new Outer();}}public static void main(String[] args) {Outer test = new Outer(5);Outer.Inner inner = test.new Inner();Outer outer = inner.getOuter();Outer outer2 = inner.newOuter();System.out.println(outer.num);System.out.println(outer2.num);}}

输出结果:

           5

           0