Java Foundation Classes in a Nutshell

empty

Indicates that the implementation of the method has an empty body. This can

be a hint to the programmer that the method may need to be overridden in a

subclass.

constant

An implementation flag that indicates that a method has a trivial implementa-

tion. Only methods with a

void retur n type can be truly empty. Any method

declar ed to retur navalue must have at least a

retur n statement. The “constant”

flag indicates that the method implementation is empty except for a

retur n

statement that retur ns a constant value. Such a method might have a body like

retur n null; or retur n false;. Like the “empty” flag, this flag indicates that a method

may need to be overridden.

default:

This flag is used with property accessor methods that read the value of a

pr operty (i.e., methods whose names begins with “get” and take no argu-

ments). The flag is followed by the default value of the property. Strictly

speaking, default property values are a specification detail. In practice, how-

ever, these defaults are not always documented, and care should be taken,

because the default values may change between implementations.

Not all property accessors have a “default:” flag. A default value is determined

by dynamically loading the class in question, instantiating it using a no-argu-

ment constructor, and then calling the method to find out what it retur ns.

This technique can be used only on classes that can be dynamically ...