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User:Alexsmail/Computer programming/How Objects should be correctly compared in Java

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Introduction

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See appendix A for formal definition.

Method along consideration

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equals()

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Object hirerachy and its state (getClass() or instanceof ?). Immutable object. Object.equals()

hashCode()

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Object.hashCode()

Natural order - compareTo()

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Comparable#compareTo()

compareTo()

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Comparable#compareTo()

Comparable#equals()

Map (Hashtable)

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Combination consideration

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equals() and hashCode()

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Object.hashCode()

equals() and compareTo()

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equals() and compareTo() and hashCode()

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HashMap, equals() and compareTo()

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TreeMap, equals() and compareTo()

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Maps, Hashtable and Set and Arrays

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HashMap's and Set's key

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Immutable. keys are Uniformly distributed.

TreeMap vs HashMap

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Sort

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QuickSort MergeSort Stable sort Comparator TreeMap


Miscellaneous

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signum function

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Sorting with Comparator

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Arrays.sort()


Appendix B

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Mathematic background

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Set Order pair Relation Relation over Set Two-place relation function function in Java Partial Order Full order Equivalence relation Equivalence class

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