java use method in another class

1class A { 
2  
3    public void a1 ( ) { 
4    } 
5 
6    private void a2 ( ) { 
7    } 
8} 
9 
10class B { 
11 
12    private A objA = new A ( ); 
13 
14    public void b1 ( ) { 
15        // Call to method a1. This works. 
16        objA.a1 (); 
17    } 
18 
19    void b2 ( ) { 
20        // Call to method a2. This will give compile error. 
21        objA.a2 (); 
22    } 
23}