4. Object Structures, Aliasing, and Encapsulation

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Explanation:(Immutability)We assume that equality for the primitive typesis defined by „==“ and for reference types bysome reasonably defined method equals.An object X is called (observationally) immutableif after termination of its constructor callany two invocationsX.m(p1,...,pn) and X.m(q1,...,qn)with pi equals qi (1≤ i ≤ n) either- yield equal results or- throw equal exceptions or- both do not terminate.A class C is called immutable if all instances of Cin any program execution are immutable.Remark:• Immutability is usually defined by prohibitingstate changes and dependency of „external“ state.• About 660 concrete classes in Java‘s standardlibrary are immutable (about 20%)13.05.13© A. Poetzsch-Heffter, TU Kaiserslautern12
Examples:1. Immutable class:(Immutability)class ImmutableList {private int head;private ImmutableList tail;boolean isempty(){ return tail == null; }}int head(){if( isempty() )throw new NoSuchElementException();return head;}ImmutableList tail(){if( isempty() )throw new NoSuchElementException();return tail;}ImmutableList cons( int i ) {ImmutableList aux = new ImmutableList();aux.head = i;aux.tail = this;return aux;}boolean equals( Object that ) {...}Objects of class ImmutableList are immutable foran appropriate method equals.13.05.13© A. Poetzsch-Heffter, TU Kaiserslautern13
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: General approaches to solve alias p
Page 15 and 16: class NotImmutableList extends Immu
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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