JAVA小白：请问这道题怎么做
class A
{
private int x=1;
class B
{
int y;
public B(int y)
{ this.y=y; }
public int f( )
{ return x+y; }
}
}
public class Outer extends A.B
{
public Outer(A a)
{ ____________________； }
}
执行 Outer o1=new Outer(new A( )); System.out.println(o1.f( )); 希望输出的结果是3。
