Abdelrahman Elkady: What is .. this ?

The 'this' keyword in Java often puzzles new programmers. It's crucial for understanding Object-Oriented Programming (OOP) and how Java manages object instances and their memory references. This thread clarifies its purpose.

Many struggle with 'this' because it ties into Java's fundamental way of handling objects: through references, not by storing entire objects in variables. Variables hold memory addresses pointing to where the actual object data resides.

Let's use a 'Cookie' class example to illustrate. When you create 'Cookie c1 = new Cookie(10, false);', 'c1' doesn't contain the cookie itself. Instead, 'c1' stores a reference, a unique memory address, to the cookie object.

To verify this, we can use 'System.identityHashCode()' to get a unique identifier for an object's memory location. Changing an object's attributes (e.g., 'c1.radius = 120;') doesn't change its memory address.

However, assigning one object reference to another, like 'c1 = c2;', makes both variables point to the exact same memory location. Any modification through 'c1' will also affect 'c2' because they refer to the same object.

The 'this' keyword inside a class method or constructor refers to the current instance of the class. It's a self-reference, allowing the object to refer to itself within its own code.

In a constructor, 'this.radius = radius;' differentiates between the instance variable 'radius' and the local parameter 'radius'. 'this' explicitly points to the instance's 'radius' variable.

When you call a method like 'getMe()' on an object, and that method returns 'this', it's returning a reference to the very object that invoked the method. This is incredibly powerful for method chaining.

Understanding 'this' is key to writing robust and correct Java code. It ensures you're manipulating the intended object instance and helps manage object state effectively within your programs.

In summary, 'this' is a reference to the current object. It's essential for distinguishing instance variables from parameters, and for allowing an object to interact with itself or return itself from methods.