Type Casting & Conversion

Converting between numeric types is either automatic (widening, no data can be lost) or must be requested explicitly (narrowing, data can be lost):

int whole = 42;
double asDouble = whole;       // widening: automatic, safe

double price = 19.99;
int asInt = (int) price;       // narrowing: explicit cast required
System.out.println(asInt);     // 19 — the decimal part is discarded

Converting between String and numbers uses the wrapper classes, not a cast:

String text = "42";
int parsed = Integer.parseInt(text);   // String -> int
String back = String.valueOf(parsed);  // int -> String

Common mistakes

• Assuming (int) price rounds — it truncates. 19.99 becomes 19, not 20. Use Math.round(price) to round instead.
• Calling Integer.parseInt() on text that isn't a valid number throws a NumberFormatException.