Widening vs Narrowing

Type Conversions in Java — The Cup Analogy • Workbook 1c, p.62-63

byte1 byte

→safe

short2 bytes

→safe

int4 bytes

→safe

long8 bytes

→safe

float4 bytes

→safe

double8 bytes

char2 bytes

→safe

int4 bytes

int
4 bytes

⇒

double
8 bytes

int x = 42;
double y = x; // automatic, safe!

✔ Widening — Java does this automatically

double
8 bytes

⇒

int
4 bytes

double price = 19.99;
int rounded = (int) price; // must cast! Loses .99!

⚠ Narrowing — Requires explicit cast, may lose data

Lost: .99 — result is 19, not 19.99!

From: To:

Select types above and click Try It!

byte b = 42;
int i = b;

✔ Safe! Widening (byte → int)

int i = 1000;
byte b = (byte) i;

⚠ Overflow! 1000 → byte = -24

double d = 9.7;
int i = (int) d;

⚠ Truncated! 9.7 → 9 (chopped, not rounded)

Widening = small → big = automatic = safe
Java handles it for you. No data is lost.
double y = myInt;

Narrowing = big → small = needs (cast) = may lose data
You must explicitly tell Java. Data may be lost!
int x = (int) myDouble;