View source for 3.2.3 Variable Declaration and Initialization

=== 3.2.3 Variable Declaration and Initialization ===
Imagine you're setting up those labeled boxes for your information. Before you can put anything ''into'' a box, you first need to:

# '''Declare''' the box (give it a name and say what kind of stuff will go in it).
# '''Initialize''' the box (put a starting piece of information in it).

'''Variable Declaration'''

* This is where you tell the computer: "Hey, I'm going to need a storage spot, and here's what I'm going to call it, and what kind of data it will hold."
* You typically specify the '''data type''' first, then the '''variable name'''.  '''Example (in plain English):'''
** <code>Number called age</code>
** <code>Text called username</code>
** <code>True/False called is_active</code>

'''Variable Initialization'''

* This is where you give the variable its very first value. It's like putting the first item into your labeled box.
* You do this using the '''assignment operator''', which is usually an equals sign (<code>=</code>).  '''Example (in plain English):'''
** <code>age = 12</code>
** <code>username = "CoderKid"</code>
** <code>is_active = true</code>

'''Putting it Together (Declaration and Initialization):'''

You can declare a variable and initialize it on the same line, which is very common:

* '''For Primitive Data Types:'''
** <code>int score = 0;</code> (A whole number variable named <code>score</code> starts at 0)
** <code>double pi = 3.14;</code> (A decimal number variable named <code>pi</code> starts at 3.14)
** <code>boolean game_over = false;</code> (A true/false variable named <code>game_over</code> starts as false)
** <code>char first_initial = 'J';</code> (A character variable named <code>first_initial</code> starts as 'J')
* '''For Reference Data Types (like Strings and Objects):'''
** <code>String greeting = "Hello!";</code> (A text variable named <code>greeting</code> stores "Hello!")
** <code>Car myCar = new Car();</code> (An object variable named <code>myCar</code> now points to a brand new <code>Car</code> object)  ''Important Note for Reference Types:'' When you declare a reference variable but don't initialize it (e.g., <code>String message;</code>), it usually starts with a special value called <code>null</code>. <code>null</code> means "no object is being pointed to right now." If you try to use a <code>null</code> variable to do something, your program will likely crash!

Understanding how to declare and initialize variables is the first step to making your programs store and work with information effectively.

'''Bibliography:'''

* '''GeeksforGeeks - Variables in Java''': https://www.geeksforgeeks.org/variables-in-java/
* '''W3Schools - JavaScript Variables''': https://www.w3schools.com/js/js_variables.asp (Good for general concept, even if JavaScript specific)
* '''Wikipedia - Variable (computer science)''': https://en.wikipedia.org/wiki/Variable_(computer_science)