Calling a method of a class without creating object of it

Question

class A{
    String z(){
        System.out.println(\"a\");
        return \"sauarbh\";
    }
}
class B{
    A a;
    A x(){
    return a;   
    }
}
public class runner         


        

Answer 1

To call:

String z(){
        System.out.println("a");
        return "sauarbh";
    }

without the object of the class A the method z has to be static:

static String z(){
        System.out.println("a");
        return "sauarbh";
    }

So change your code as following:

class A{
    static String z(){
        System.out.println("a");
        return "sauarbh";
    }
}
class B{
    A a;
    A x(){
    return a;   
    }
}
public class runner {
    public static void main(String[] args) {
         B b = new B();
         b.x();
         A.z();
    }
}

Output :

a

Answer 2

Class B method x() is not returning new object of A. Instead you are returning object of Class A with null value.

A a; // value of a is null 
A x() {
    return a;
}

In runner class

A a2=b.x(); // b.x() will return a, which is null. so A a2=null
a2.z();    // Equivalent to null.z() throws NullPointerException 

Make below changes in your Class B code:

class B{
    A a;
    A x(){
    return new A();// return new object of Class A;   
    }
}

or

class B{
    A a= new A(); // Initialize Class A with new object 
    A x(){
    return a;   
    }
}

Answer 3

Yes without instantiate the class if you want to call the method you should use static key word.

What are you doing here?

You are indirectly try to get instance of A. But this case you will get NullPointerException since you just return only a reference(variable) of A

B b = new B();
A a2=b.x();
a2.z(); // NullPointerException from here

NPE?

class B{
  A a;
  A x(){
   return a;   // you just return the reference 
   // it should be return new A();
  }
 }

For your edit:

Take a look at insert() method. It is creating Person instance.