Type Casting

Type casting means converting a value from one type to another. Java has two kinds: implicit (widening) casting, which happens automatically when no data can be lost, and explicit (narrowing) casting, which you must write yourself because it risks losing information.

int wholeNumber = 10;
double decimalNumber = wholeNumber; // implicit widening
System.out.println(decimalNumber);  // 10.0

Going the other way — from a larger or more precise type to a smaller one, like double to int — is called narrowing, and Java requires you to write an explicit cast: the target type in parentheses right before the value. This forces you to acknowledge that some information might be lost.

double price = 9.99;
int wholePrice = (int) price;
System.out.println(wholePrice); // 9

Precision loss isn't limited to decimals: casting a whole-number type into a smaller one can also lose data if the value doesn't fit. When that happens, the number can "wrap around" into a completely unexpected — even negative — result, which is a common source of subtle bugs.

long big = 3000000000L;
int smaller = (int) big;
System.out.println(smaller); // overflows to an unexpected, incorrect number

Converting a larger type into a smaller one, such as double to int, is called ____ casting and requires an explicit cast.

What does casting the double 9.99 to an int produce?

Widening a value, such as converting an int to a double, happens automatically in Java.