How is passing arguments by reference implemented in programming?

In Java, passing arguments by reference is not directly supported — all arguments are passed by value. However, it is important to understand that for objects, a copy of the reference to the object is passed, not the object itself.

This means that inside the method, you can modify the state of the object that the parameter refers to, and these changes will be visible outside. But if you reassign the parameter to another object, it will not affect the reference outside the method.

Example:

class MyObject {
    int value;
}

void modify(MyObject obj) {
    obj.value = 10; // changes the state of the object
    obj = new MyObject(); // reassigns the local copy of the reference
    obj.value = 20; // this will not affect the object outside the method
}

MyObject o = new MyObject();
modify(o);
System.out.println(o.value); // will print 10

Thus, in Java, you can modify the contents of objects through parameters, but you cannot change the actual reference to the object in the calling code.