Method Signature

8.4.2 Method Signature

Two methods have the same signature if they have the same name and argument types.

Two method or constructor declarations M and N have the same argument types if all of the following conditions hold:

•They have the same number of formal parameters (possibly zero)

•They have the same number of type parameters (possibly zero)

•Let A1, ..., An be the type parameters of M and let B1, ..., Bn be the type parameters of N. After renaming each occurrence of a Bi in N's type to Ai, the bounds of corresponding type variables are the same, and the formal parameter types of M and N are the same.

The signature of a method m1 is a subsignature of the signature of a method m2 if either:

•m2 has the same signature as m1, or

•the signature of m1 is the same as the erasure (§4.6) of the signature of m2.

Two method signatures m1 and m2 are override-equivalent iff either m1 is a subsignature of m2 or m2 is a subsignature of m1.

It is a compile-time error to declare two methods with override-equivalent signatures in a class.

Example 8.4.2-1. Override-Equivalent Signatures

class Point { int x, y;

abstract void move(int dx, int dy);

void move(int dx, int dy) { x += dx; y += dy; }

}

This program causes a compile-time error because it declares two move methods with the same (and hence, override-equivalent) signature. This is an error even though one of the declarations is abstract.

The notion of subsignature is designed to express a relationship between two methods whose signatures are not identical, but in which one may override the other. Specifically, it allows a method whose signature does not use generic types to override any generified version of that method. This is important so that library designers may freely generify methods independently of clients that define subclasses or subinterfaces of the library.

Consider the example:

class CollectionConverter {

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