What is a variable?
A variable is a labelled box in the computer's memory. You put a value in the box, give the box a name, and later refer to the value by its name. Variables let you store user input, intermediate results and program state without hard-coding numbers and strings everywhere.
Declaring a variable
In Java you declare a variable with the syntax shown below. Choose names that describe what the value represents: userAge is far better than x. Stick to one naming style across a project (camelCase, snake_case…) so the code stays consistent.
int age = 25;
String name = "Aman";
boolean isStudent = true;
System.out.println(name + " " + age);Reassignment and scope
Most variables can be reassigned later — the box stays, the contents change. The places in your code where a variable is visible is called its scope. Variables declared inside a function are usually only visible inside that function, which keeps programs predictable as they grow.