15.11.2

Compile Time Step 2: Determine Method Signature

EXPRESSIONS

class Test extends Doubler {

public static long two(long j) {return j+j; }

public static void main(String[] args) {

System.out.println(two(3));

System.out.println(Doubler.two(3)); //

compile time error

}

}

for the method invocation

two(1)

 within class

Doubler

, there are two accessible

methods named

two

, but only the second one is applicable, and so that is the one

invoked at run time. For the method invocation

two(3)

 within class

Test

, there

are two applicable methods, but only the one in class

Test

 is accessible, and so

that is the one to be invoked at run time (the argument

3

 is converted to type

long

). For the method invocation

Doubler.two(3)

, the class

Doubler

, not class

Test

, is searched for methods named

two

; the only applicable method is not

accessible, and so this method invocation causes a compile time error.

Another example is:

class ColoredPoint {

int x, y;

byte color;

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

}

class Test {

public static void main(String[] args) {

ColoredPoint cp = new ColoredPoint();

byte color = 37;

cp.setColor(color);

cp.setColor(37);

//

compile time error

}

}

Here, a compile time error occurs for the second invocation of

setColor

, because

no applicable method can be found at compile time. The type of the literal

37

 is

int

, and

int

 cannot be converted to

byte

 by method invocation conversion.

Assignment conversion, which is used in the initialization of the variable

color

,

performs an implicit conversion of the constant from type

int

 to

byte

, which is

permitted because the value

37

 is small enough to be represented in type

byte

; but

such a conversion is not allowed for method invocation conversion.

If the method

setColor

 had, however, been declared to take an

int

 instead of

a

byte

, then both method invocations would be correct; the first invocation would

be allowed because method invocation conversion does permit a widening conver 

sion from

byte

 to

int

. However, a narrowing cast would then be required in the

body of

setColor

:

326