5.3 Method Invocation Conversion

Method invocation conversion is applied to each argument value in a method or constructor invocation (§15.8, §15.11): the type of the argument expression must be converted to the type of the corresponding parameter. Method invocation contexts allow the use of an identity conversion (§5.1.1), a widening primitive conversion (§5.1.2), or a widening reference conversion (§5.1.4).

Method invocation conversions specifically do not include the implicit narrowing of integer constants which is part of assignment conversion (§5.2). The Java designers felt that including these implicit narrowing conversions would add additional complexity to the overloaded method matching resolution process (§15.11.2). Thus, the example:

class Test {

	static int m(byte a, int b) { return a+b; }


	static int m(short a, short b) { return a-b; }

	public static void main(String[] args) {
		System.out.println(m(12, 2));										// compile-time error
	}

}

causes a compile-time error because the integer literals 12 and 2 have type int, so neither method m matches under the rules of (§15.11.2). A language that included implicit narrowing of integer constants would need additional rules to resolve cases like this example.