The Java Language Specification, Third Edition

EXPRESSIONS Compile-Time Step 3: Is the Chosen Method Appropriate? 15.12.3
because the old binary file for Test still has the descriptor “one parameter, whose
type is Point; void” associated with the method call cp.adopt(cp2). If the
source code for Test is recompiled, the compiler will then discover that there are
now two applicable adopt methods, and that the signature for the more specific
one is “one parameter, whose type is ColoredPoint; void”; running the program
will then produce the desired output:
cp: (3,3,green)
With forethought about such problems, the maintainer of the points package
could fix the ColoredPoint class to work with both newly compiled and old
code, by adding defensive code to the old adopt method for the sake of old code
that still invokes it on ColoredPoint arguments:
public void adopt(Point p) {
if (p instanceof ColoredPoint)
color = ((ColoredPoint)p).color;
x = p.x; y = p.y;
}
Ideally, source code should be recompiled whenever code that it depends on is
changed. However, in an environment where different classes are maintained by
different organizations, this is not always feasible. Defensive programming with
careful attention to the problems of class evolution can make upgraded code much
more robust. See §13 for a detailed discussion of binary compatibility and type
evolution.
15.12.3 Compile-Time Step 3: Is the Chosen Method Appropriate?
If there is a most specific method declaration for a method invocation, it is called
the compile-time declaration for the method invocation. Three further checks
must be made on the compile-time declaration:
• If the method invocation has, before the left parenthesis, a MethodName of
the form Identifier, and the method is an instance method, then:
DRAFT
◆ If the invocation appears within a static context (§8.1.3), then a compiletime
error occurs. (The reason is that a method invocation of this form cannot
be used to invoke an instance method in places where this (§15.8.3) is
not defined.)
◆ Otherwise, let C be the innermost enclosing class of which the method is a
member. If the invocation is not directly enclosed by C or an inner class of
C, then a compile-time error occurs
• If the method invocation has, before the left parenthesis, a MethodName of
the form TypeName.Identifier, or if the method invocation , before the left
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