Introduction

Java supports references, but it doesn't allow pass by references. Here, we're going to play with Java to understand the concepts better.

References

Let's think of a simple object, such as a string:

String name = "Paul Stanley";

Whenever an object is created, it's stored in the heap, and the reference to the object is always used to work with it.

Above, the variable "name" is the reference and it points to a String object. If it wasn't set to anything, it'd just point to null.

Let's see how two variables may point to the same object:

String name = "Paul Stanley";
String name2 = name;

name == name2; // true, as the two references are equal (they point to the same thing)

In memory, only one object has been created, but there are 2 references which point to it. If at any given time, those variables (references) get removed from the stack, and if no other variable points to the object, the object would be removed from memory by the garbage collector.

The dot (.) operator is used to work with the object through the reference:

Person a = new Person();
a.setName("Paul Stanley");

Passing Arguments

Java only supports pass by values, and it doesn't support pass by references.

Let's see it in action by creating an object and passing it to a method:

Person a = new Person("A");

test(a); // only the value of reference "a" is only sent to the method, not the reference itself!

a.getName(); // "A" <- It's not "B." Pass by reference would have altered the value of reference "a."

...

public static void test(Person a) {
    a = new Person("B"); // setting the reference "a" to a new object
}

Whenever, we passed the reference "a" to the method, the reference's value got passed to the method where another reference was created to hold it. The new reference can refer to any other object as programmed.

The old reference's value was used to create the new reference, which implies a pass by value, not reference.

nahiyan/readme.md

Introduction

References

Passing Arguments