EXPRESSIONS

Compile Time Step 2: Determine Method Signature

15.11.2

void setColor(int color) { this.color = (byte)color; }

15.11.2.2

Choose the Most Specific Method

If more than one method is both accessible and applicable to a method invocation,

it is necessary to choose one to provide the descriptor for the run time method dis 

patch. Java uses the rule that the

most specific

 method is chosen.

The informal intuition is that one method declaration is more specific than

another if any invocation handled by the first method could be passed on to the

other one without a compile time type error.

The precise definition is as follows. Let

m

 be a name and suppose that there

are two declarations of methods named

m

, each having

n

 parameters. Suppose that

one declaration appears within a class or interface

T

 and that the types of the

parameters are

T1

, . . . ,

Tn

; suppose moreover that the other declaration appears

within a class or interface

U

 and that the types of the parameters are

U1

, . . . ,

Un

.

Then the method

m

 declared in

T

 is

more specific

 than the method

m

 declared in

U

if and only if both of the following are true:

T

 can be converted to

U

 by method invocation conversion.

Tj

 can be converted to

Uj

 by method invocation conversion, for all

j

 from

1

to

n

.

A method is said to be

maximally specific

 for a method invocation if it is

applicable and accessible and there is no other applicable and accessible method

that is more specific.

If there is exactly one maximally specific method, then it is in fact

the most

specific

 method; it is necessarily more specific than any other method that is appli 

cable and accessible. It is then subjected to some further compile time checks as

described in  15.11.3.

It is possible that no method is the most specific, because there are two or

more maximally specific method declarations. In this case, we say that the method

invocation is

ambiguous

, and a compile time error occurs.

15.11.2.3

Example: Overloading Ambiguity

Consider the example:

class Point { int x, y; }

class ColoredPoint extends Point { int color; }

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