Does Java pass by reference or pass by value?

Hi guys this is a very good topic in java people generally confused on it. Here I am trying to explain how Java is always use pass-by-value.

The Java Spec says that everything in Java is pass-by-value. There is no such thing as "pass-by-reference" in Java.

The key point to understand is when we are passing an object in a method than we are actually passing the address of the object. Actually it’s a copy of bit of that object.

When we pass an Object into a method we are passing the Object reference and not the Object itself.

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Java example –

In below example we are passing the primitive variable number than its just passing a copy of bit representation of number that’s why the actual value unchanged in main method.

Code snippet-

/**

 * @author Manoj

 */

public class ReferenceTest {

   public static void main(String[] args) {

       int number =1;

       ReferenceTest referenceTest = new ReferenceTest();

       System.out.println(number); //prints 1

       referenceTest.modify(number);

       System.out.println(number); //prints 1

   }

   private void modify (int number) {

       number = number+1;

       System.out.println(number); // print 2

   }

}

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Similarly in below code we are using a static variable but again the value is unchanged in main method because it’s just passing a copy.

Code snippet-

/**

 * @author Manoj

 */

public class ReferenceTest {

   static int number = 11;

      

   public static void main(String[] args) {

             

       ReferenceTest referenceTest = new ReferenceTest();

       System.out.println(number); //prints 11

       referenceTest.modify(number);

       System.out.println(number); //prints 11

   }

   private void modify (int number) {

       number = number+10;

       System.out.println(number); // print 21

   }

}

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In below code we are taking Reference object to elaborate the concept of copy of value.

Code snippet-

/**

 * @author Manoj

 */

public class ReferenceTest {

   Reference reference = new Reference();

   public static void main(String[] args) {

       ReferenceTest referenceTest = new ReferenceTest();

       System.out.println(referenceTest.reference.refNumber); //prints 28

       referenceTest.modify(referenceTest.reference);

       System.out.println(referenceTest.reference.refNumber); //prints 99

   }

   private void modify (Reference reference) {

       reference.refNumber = 99; // here we are updating the actual value

       System.out.println(reference.refNumber); // print 99

       reference = new Reference();

       reference.refNumber = 420;

       System.out.println(reference.refNumber); //420

   }

}

class Reference {

    int refNumber = 28;

}