Variables

A variable in Java is a named storage location in memory that holds a value which can be changed during program execution. Variables allow you to store, retrieve, and manipulate data in your programs.

Properties

• Has a specific data type (e.g., int, double, String)
• Has a name (identifier)
• Can store a value (which may change during program execution)
• Has a scope (where it can be accessed in the code)

Declaration vs. Definition

Term	Description	Example
Declaration	Introducing a variable’s name and type to the compiler, without necessarily assigning a value	int x;
Definition	Both declaring a variable and assigning it an initial value	int x = 10;

Basic Assignment

The basic way to assign a value is with the assignment operator (=):

// Simple variable declaration and assignment
int age = 25;
double salary = 75000.50;
char grade = 'A';
boolean isActive = true;
String name = "John Smith";

Assignment with Expressions

You can assign the result of an expression to a variable:

int a = 5;
int b = 10;
int sum = a + b;  // sum equals 15
int product = a * b;  // product equals 50
double result = (a + b) / 2.0;  // result equals 7.5

Best Practices

1. Initialize variables when declaring them, unless there’s a specific reason not to
2. Use meaningful variable names that describe what the variable represents
3. Limit variable scope to where it’s needed
4. Use final for values that shouldn’t change
5. Be careful with type conversions to avoid data loss