Java Reference
In-Depth Information
Shape instance stored in an array. When Shape 's draw() method is called for an
arrayinstance,itisthe Circle 's, Rectangle 'sorother Shape instance's draw()
methodthatgetscalled.Wesaythattherearemanyformsof Shape 's draw() method,
or that this method is polymorphic.
Java supports four kinds of polymorphism:
Coercion :Anoperationservesmultipletypesthroughimplicittypeconversion.
andtheotheroperandisafloating-pointvalue,thecompiler coerces (implicitly
type to the superclass type, to restrict operations to those of the superclass.
Overloading :Thesameoperatorsymbolormethodnamecanbeusedindiffer-
entcontexts.Forexample, + canbeusedtoperformintegeraddition,floating-
Also, multiple methods having the same name can appear in a class (through
declaration and/or inheritance).
Parametric :Withinaclassdeclaration,afieldnamecanassociatewithdifferent
types and a method name can associate with different parameter and return
types. The field and method can then take on different types in each class in-
stance. For example, a field might be of type java.lang.Integer and a
methodmightreturnan Integer referenceinoneclassinstance,andthesame
field might be of type String and the same method might return a String
generics, which I will discuss in Chapter 3 .
Subtype :Atypecanserveasanothertype'ssubtype.Whenasubtypeinstance
instance results in the subtype's version of that operation executing. For ex-
ample, suppose that Circle is a subclass of Point , and that both classes
contain a draw() method. Assigning a Circle instance to a variable of
type Point ,andthencallingthe draw() methodviathisvariable,resultsin
Circle 's draw() methodbeingcalled.Subtypepolymorphismpartnerswith
implementation inheritance.
Many developers do not regard coercion and overloading as valid kinds of poly-
morphism. They see coercion and overloading as nothing more than type conversions
Search WWH ::

Custom Search