Type Casting

Type Casting

Type casting is converting one data type into another. Java has two kinds: widening (automatic) and narrowing (manual).

Widening casting (automatic)

Converting a smaller type to a larger type happens automatically:

int myInt = 9;
double myDouble = myInt; // Automatic: int -> double
System.out.println(myDouble); // 9.0

Order of automatic conversion:

byte -> short -> char -> int -> long -> float -> double

Narrowing casting (manual)

Converting a larger type to a smaller type must be done manually by placing the type in parentheses:

double myDouble = 9.78d;
int myInt = (int) myDouble; // Manual: double -> int
System.out.println(myInt); // 9

Casting to string and back

String s = Integer.toString(123);      // "123"
int n = Integer.parseInt("456");       // 456

Why casting matters

Widening is safe because no data is lost. Narrowing can lose data: converting 9.78 to an int drops the decimal and gives 9.

TL;DR

• Widening (smaller to larger) happens automatically.
• Narrowing (larger to smaller) needs an explicit cast in parentheses.
• Use Integer.parseInt() and Integer.toString() to convert between String and int.