4. Object Structures, Aliasing, and Encapsulation

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Leaking:• Leaking occurs when data structure passes areference to an object which is supposed to beinternal to the outside• Leaking often happens by mistake.• Problem: Alias can be used to by-pass interfaceof data structure.list1array:next:arrayclass ArrayList {private int[ ] array;private int next;public int[ ] getElems( ){ return array; }…}13.05.13© A. Poetzsch-Heffter, TU Kaiserslautern10
General approaches to solve alias problems:- Support aliasing, but disable modifications(avoids undesirable aspects (1.), (2.) and (4.)from above)- Control aliasing and access4.2 ImmutabilityReferential transparency means that the holder ofan object reference R- does not have to care about aliases of R,- in particular, cannot observe whether aliases of Rexist (by using R).Techniques to achieve referential transparency:- immutability- uniquenessAssumption:To keep the following definitions simpler, we assumethat reading and writing to instance variables of anobject X can only be done by methods of X‘s class(possibly inherited methods).That is, objects can only be observed by methodinvocation.13.05.13© A. Poetzsch-Heffter, TU Kaiserslautern11
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: Forms of Alias Creation:Capturing:
Page 13 and 14: Examples:1. Immutable class:(Immuta
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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