Collections II Christian Rodríguez Bustos Object Oriented Programming

Collections

Agenda

HashMap Class

TreeMap Class

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HashSet Class

HashMap

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HashMap Class

Hash Maps are dictionary type collections

Hash Maps give us direct access to a given object based on a unique key value

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HashMap Class example

Unique key value

251032

235645

202978

354687

studentList HashMap

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HashMap instantiation

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HashMap instantiation

Object Key Type

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HashMap instantiation

Object Key Type

Object (Value)

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Put method example

Object Key Type Object (Value)

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Put / Get methods examples

Object Key Type

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If the key is not found, a null value will be returned

Contains Value / Contains Key methods examples

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Is Empty / Size methods examples

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Key Set / Values methods examples

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Remove methods examples

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TreeMap

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TreeMap

TreeMap

• Objects are automatically retrieved from the collection in ascending key (sorted) order.

HashMap

• There is no guarantee as to the order in which items will be retrieved.

TreeMaps and HashMaps are instantiated using the same syntax

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Testing HashMaps and TreeMaps

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Iterating through HashMaps and TreeMaps

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Test Program output

Unsorted

Sorted

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HashSet

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HashSet Methods I

Instantiation

Add

Contains?

HashSet Methods II

Size Remove?

HashSets have not a get method

HashSets are unsorted

We need an Iterator for getting elements

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Testing HashSet

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Test Program output

Unsorted outputs

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References

[Barker] J. Barker, Beginning Java Objects: From Concepts To Code, Second Edition, Apress, 2005. [Oracle] The HashMap Class Available: http://download.oracle.com/javase/6/docs/api/java/util/HashMap.html, 2011 [Oracle] The HashSet Class Available: http://download.oracle.com/javase/6/docs/api/java/util/HashSet.html, 2011 [Oracle] The TreeMap Class Available: http://download.oracle.com/javase/6/docs/api/java/util/TreeMap.html, 2011

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