java use class in another class code example

Example 1: can we create a class inside a class in java

Yes you can

class OuterClass {
   class InnerClass {
   }
}

Example 2: java use method in another class

class A { 
  
    public void a1 ( ) { 
    } 
 
    private void a2 ( ) { 
    } 
} 
 
class B { 
 
    private A objA = new A ( ); 
 
    public void b1 ( ) { 
        // Call to method a1. This works. 
        objA.a1 (); 
    } 
 
    void b2 ( ) { 
        // Call to method a2. This will give compile error. 
        objA.a2 (); 
    } 
}