how to use methods from another class in java code example

Example 1: 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 (); 
    } 
}

Example 2: how to access methods from another class in java

public class Alpha {
     public void DoSomethingAlpha() {
          Beta cbeta = new Beta();
          cbeta.DoSomethingBeta();  //?
     }
}

Example 3: how to access methods from another class in java

public class Alpha extends Beta{
     public void DoSomethingAlpha() {
          DoSomethingBeta();  //?
     }
}

Example 4: how to access methods from another class in java

Beta.DoSomethingBeta();