Q.Differentiate between a variable and a constant in Java, giving one example of each declaration.

Both are named data holders, but one is allowed to change and the other is not.

Variable. A variable is a named box in memory that stores a value which may be changed any number of times while the program runs. It must be declared with a data type before use:

int marks = 85;
marks = 90;          // allowed — a variable's value can change

Constant. A constant is a named value that must not change after it is first set. In Java it is created using the keyword final, and by convention its name is written in capitals:

final double PI = 3.14159;
// PI = 3.15;       // NOT allowed — causes a compile-time error

Key differences:

Thinking final is optional decoration — it actively prevents reassignment, and attempting to change a final value is a compil …