4. Object Structures, Aliasing, and Encapsulation

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3. Immutable objects must not depend on globalvariables:class Global {public static int a = 5;public static int getA(){return a;}}class Immutable2 {public int alwaysTheSame() {return Global.getA();}}Immutable2-objects are not immutable!The example demonstrates that mutability can depend on global state.13.05.13© A. Poetzsch-Heffter, TU Kaiserslautern16
4. Immutable objects with varying I/O-behavior:final class Immutable3 {}private int state;public int alwaysTheSame() {}System.out.println(state++);return 47;5. Immutable objects where state changes canmake sense:Typical example: Initialization of instancevariables on demand, i.e., not by the constructor,but prior to first use.Techniques for Realizing Immutability:Immutability is implemented using different techniques:- Access and inheritance restrictions- Immutable state (local and reachable state)- Prohibition of access to global state (direct orvia methods)13.05.13© A. Poetzsch-Heffter, TU Kaiserslautern17
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 and 14: Examples:1. Immutable class:(Immuta
Page 15: class NotImmutableList extends Immu
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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