9.3.2 Examples of Field Declarations

The following example illustrates some (possibly subtle) points about field declarations.

9.3.2.1 Ambiguous Inherited Fields

If two fields with the same name are inherited by an interface because, for example, two of its direct superinterfaces declare fields with that name, then a single ambiguous member results. Any use of this ambiguous member will result in a compile-time error. Thus in the example:

interface BaseColors {
	int RED = 1, GREEN = 2, BLUE = 4;
}


interface RainbowColors extends BaseColors {
	int YELLOW = 3, ORANGE = 5, INDIGO = 6, VIOLET = 7;
}


interface PrintColors extends BaseColors {
	int YELLOW = 8, CYAN = 16, MAGENTA = 32;
}


interface LotsOfColors extends RainbowColors, PrintColors {
	int FUCHSIA = 17, VERMILION = 43, CHARTREUSE = RED+90;
}

the interface LotsOfColors inherits two fields named YELLOW. This is all right as long as the interface does not contain any reference by simple name to the field YELLOW. (Such a reference could occur within a variable initializer for a field.)

Even if interface PrintColors were to give the value 3 to YELLOW rather than the value 8, a reference to field YELLOW within interface LotsOfColors would still be considered ambiguous.

9.3.2.2 Multiply Inherited Fields

If a single field is inherited multiple times from the same interface because, for example, both this interface and one of this interface's direct superinterfaces extend the interface that declares the field, then only a single member results. This situation does not in itself cause a compile-time error.

In the example in the previous section, the fields RED, GREEN, and BLUE are inherited by interface LotsOfColors in more than one way, through interface RainbowColors and also through interface PrintColors, but the reference to field RED in interface LotsOfColors is not considered ambiguous because only one actual declaration of the field RED is involved.