5.3

Method Invocation Conversion

CONVERSIONS AND PROMOTIONS

The value of

pvec

 cannot be assigned to

cpvec

, because not every reference

that could be the value of an expression of type

ColoredPoint

 can correctly

be the value of a variable of type

Point

. If the value of

pvec

 at run time were

a reference to an instance of

Point[]

, and the assignment to

cpvec

 were

allowed, a simple reference to a component of

cpvec

, say,

cpvec[0]

, could

return a

Point

, and a

Point

 is not a

ColoredPoint

. Thus to allow such an

assignment would allow a violation of the type system. A cast may be used

( 5.4,  15.15) to ensure that

pvec

 references a

ColoredPoint[]

:

cpvec = (ColoredPoint[])pvec;

//

okay, but may throw an

//

exception at run time

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 con 

texts allow the use of an identity conversion ( 5.1.1), a widening primitive conver 

sion ( 5.1.2), or a widening reference conversion ( 5.1.4).

Method invocation conversions specifically do not include the implicit nar 

rowing 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.

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