CODEWITHSUNDEEP
java
subodh
subodh

Reputation: 6158

In case of an Atomic classes, how does Java manage the call by value?

I am currently working on atomic classes and I am unable to track whether it is "call by value" or "call by reference". I understand that Java does not allow call by reference and that it is only and only call by value. But in case of atomic classes, it seems to be call by reference. Can you share your thoughts with me?

Upvotes: 0

Views: 202

Answers (3)

Jack Edmonds
Jack Edmonds

Reputation: 33171

In Java, method calls are pass by value. But when you pass an object to a function, you are actually passing a reference to the object by value. This means that if you do something like

public static int f(AtomicInteger x){
    x=new AtomicInteger(4);
    return x.get();
}
public static int g(AtomicInteger x){
    x.set(5);
    return x.get();
}
public static void main(String[] args){
    AtomicInteger y=new AtomicInteger(3);
    System.out.println(f(y));
    System.out.println(y.get());
    System.out.println(g(y));
    System.out.println(y.get());
}

You will get the result

4
3
5
5

Because you passed y by value. f did not change the value of the object y, nor did g. However g did change the internal state of y.

See Parameter passing in Java for more details.

Upvotes: 0

Tom Hawtin - tackline
Tom Hawtin - tackline

Reputation: 147164

Java passes references by value. Your variable is of type reference to AtomicInteger. So when you call a method the reference is copied, but the object is not. Indeed, Java has no standard way of copying objects (there is the protected Object.clone, but that is evil).

Upvotes: 1

Bozho
Bozho

Reputation: 597106

It's called pass by value/reference, and it concerns passing arguments to methods.

Atomic classes are no exception to the pass-by-value:

public void method1() {
    AtomicInteger atomic = new AtomicInteger(5);
    method2(atomic);
    System.out.println(atomic.get()); // prints 5
}

public void method2(AtomicInteger atomic) {
   atomic = new AtomicInteger(7); // reassign, but this does not affect metod1
}

Upvotes: 3

Related Questions