Basic HTML version of Foils prepared Sept 21 1998

Foil 28 Comments on Casting

From Java Tutorial 98- 2: Java Language and Object Oriented Techniques NAVO Tutorial -- Sept 23 1998. by Geoffrey C. Fox, Nancy McCracken
Casting (type conversion) is supported between types and class types. Syntax:
  • (classname)reference
Two forms of casting are possible: widening and narrowing
Widening, where the subclass is used as an instance of the superclass, is performed implicitly
Narrowing, where the superclass is used as an instance of the subclass, must be performed explicitly
Given Parent: Dot -> DrawableDot (Child):
  • Widening: An instance of DrawableDot is used as an instance of Dot
  • Narrowing: An instance of Dot is used as an instance of DrawableDot
Casting between sibling classes is a compile-time error

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