Styjun

I am facing a problem as my class variable gets automatically updated with the latest value. But I want separate value for each of the object.

public class B 

 public String state; 

 public B() 
 this.state = "new";
 

 public void firstMethod()

 this.state = "first"; 

 

 public void secondMethod() 

 this.state = "second";
 




public abstract class C 

 public B b; 

 public C(B service) 
 this.b = service;
 

 public abstract void execute();



public static void main(String[] args) 
 B b = new B();
 C c = new C(b) 
 @Override
 public void execute() 
 b.firstMethod();

 
 ; 

 C c1 = new C(b) 
 @Override
 public void execute() 
 b.secondMethod();

 
 ; 

 c.execute();
 c1.execute();
 System.out.println(c.b.state);

 System.out.println(c1.b.state);

I am getting c and c1 both state equal to "second". I know if I create two separate B object i.e. b1 and b2 and pass those in c and c1 while initializing then it would give me different result as I am expecting. But is there any way to get c.state as "first" and c1.state as "second" with passing the same object to both c and c1?

Your c and c1 share the exact same B object, namely b.

Since the state we are discussing belongs to b, there is only one of them - called b.state.

If you want state to be different, you cannot use the same B object with both C objects.

This likely boils down to a misunderstanding of the reference semantics of assignment and parameter passing. Neither assignment nor parameter-passing makes a copy of an object.

But is there any way to get c.state as "first" and c1.state as
"second" with passing the same object to both c and c1?

This could not possibly work. Suppose a single B object could somehow have any number of values of state. Whenever you wrote b.state, how would the system know which one you meant?

Well, that's not entirely true as I wrote it. If the constructor of C only used its B object to make an entirely new copy, such that it kept the copy rather than the original, then you'd achieve the effect; there would be three B objects in the world, the original, the copy made by c, and the copy made by c1. But that has no advantage here over just passing in separate B instances to begin with.

You used the same instance of B class into your 2 objects, so your state variable will always get updated by the last called method, you need to use another instance of B to have two separated state property.