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Foil 15 Comments on Casting

From Jan 27 Delivered Lecture for Course CPS616 -- Java Lecture 2 -- Basic Applets and Objects CPS616 spring 1997 -- Jan 27 1997. by Nancy McCracken * See also color IMAGE
Secs 90.7
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
Northeast Parallel Architectures Center, Syracuse University, npac@npac.syr.edu

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