4. Object Structures, Aliasing, and Encapsulation

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class ImmutableList { // continued...boolean equals( <strong>Object</strong> that ) {if( that == null ||!(that instanceof ImmutableList )return false;ImmutableList tl = (ImmutableList) that;if( isempty() ) {return that.isempty();} else if( that.isempty() ) {return false;} else {return ( this.head == that.head )&& tail().equals( that.tail() );}}}2. Immutability <strong>and</strong> inheritance:There may be scenarios in which objects of typeImmutableList are not immutable:...static boolean somemethod( ImmutableList il ){if( !il.isempty() ) {return il.head() == il.head();} else return true;}13.05.13© A. Poetzsch-Heffter, TU Kaiserslautern14
class NotImmutableList extends ImmutableList{private boolean flag;boolean isempty(){ return false; }int head(){flag = !flag;if( flag ){return 7;} else return 9;}}ImmutableList cons( int i ) {return new NotImmutableList();}...ImmutableList il = new NotImmutableList();il.cons(7).cons(9);System.out.println( somemethod(il) );...The example demonstrates that subclasses can breach immutability.13.05.13© A. Poetzsch-Heffter, TU Kaiserslautern15
Page 1 and 2: 4. Object Structures, Aliasing,and
Page 3 and 4: Examples:(Object structures)1. A ve
Page 5 and 6: Problems:• Structural integrity (
Page 7 and 8: Undesirable Aspects of Aliasing:1.
Page 9 and 10: Forms of Alias Creation:Capturing:
Page 11 and 12: General approaches to solve alias p
Page 13: Examples:1. Immutable class:(Immuta
Page 17 and 18: 4. Immutable objects with varying I
Page 19 and 20: 4.3 Alias Control and Encapsulation
Page 21 and 22: Roles in Object Structures:• Inte
Page 23 and 24: 2. Representations (rep mode):• E
Page 25 and 26: Meaning of alias modes:• Alias mo
Page 27 and 28: Programming Discipline (simplified)
Page 29 and 30: Example:(Representation exposure)-
Page 31 and 32: 4.3.2 Type-based EncapsulationType
Page 33 and 34: Connection with type systems:• Ea
Page 35 and 36: Scenarios in which references are i
Page 37 and 38: Remark:• The behavior of anonymou
Page 39 and 40: Further Structuring Techniques:Diff
Page 41 and 42: Cluster:Let G be the undirected gra
Page 43 and 44: Ownership:Idea:• Introduce an own
Page 45: The ownership relation is a binary

4. Object Structures, Aliasing, and Encapsulation

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