MELJUN CORTES JAVA_Collections

8/10/2019 MELJUN CORTES JAVA_Collections

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The CollectionsFramework

Java Data Structures

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What You Should Learn

DefinitionTypes of Collections

Using CollectionsIteratingCopyingCollections in Java 1.5


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Definition

Collectionobject that groups multiple elements into

a single unitan array is a collection


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Definition

Collections Frameworkunified architecture for representing and

manipulating collections


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Definition

Collections FrameworkThree Elements:

Interfaceshow you handle the collectionImplementations

the classes that actually hold the data

Algorithmsuseful routines


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The Java CollectionsFramework

Interfaces

Collection

List Set Queue Map


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The Java CollectionsFramework

Collectionsuper type of List, Set and Queue

Liststores elements in the order they were added, similarto an array only growable

Setstores only unique elements, no duplicates

Queue

stores elements in preparation for processing, usuallyeither by FIFO or by priorityMap

stores key-value pairs, like for a lookup table


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Collection

Defines commonmethods

add

addAllremoveremoveAllclear

containscontainsAll

isEmptysizetoArrayiterator


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Lists

growable array Elements ordered in the sequence theywere added.Allows you to get and set using and index

myList.set(4, Barracuda);

String fish = myList.get(4);


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Lists

Implementations:ArrayList

LinkedListVector


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Lists

ArrayListbacked by an Object arrayfast in getting and setting elementsslow in inserting and removing


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Lists

LinkedListslow in getting and setting elementsfast in inserting and removing


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Lists

VectorJust like an ArrayList only all methods aresynchronized.Was the only list available prior to Java1.1.ArrayList is preferred to Vector because

programmer has control oversynchronization.


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Sets

No duplicatesMaintains its o w n order

Same interface as Collection


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Sets

Implementations:HashSet

TreeSet


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Sets

TreeSetStores data in a binarytree to search forduplicates.

Sorted naturally Implements SortedSetinterface


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Queues

For holding elements prior to processing.Typically FIFO but may be ordered bypriorityImplementations:

LinkedList (FIFO)PriorityQueue


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Queues

Methodselementoffer

Peekpollremove


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Maps

An object that maps keys to valuesKeys are unique

Key (User ID String) Value (some object)

C234D7

A497X3

B252M5

R567B7


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Maps

Using a map:

myMap.put(T234Y9, someObject);

Getting from a map:

myMap.get(T234Y9);


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Maps

Implementations:HashMap

TreeMapHashTable


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Maps

HashMapKeys are ordered using a hash tableimplementation, similar to HashSet.

Keys are not sorted naturally.


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Maps

TreeMapUses a binary tree to order keys.Keys are sorted naturally.


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Maps

HashTableJust like an HashMap only all methods aresynchronized.

Was the only map available prior to Java 1.1.HashMap is preferred to HashTable becauseprogrammer has control over synchronization.


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Maps

HashMap vs. TreeMapHashMap is usually faster than TreeMap.Use TreeMap if you need keys to be sorted.


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Iterator

Prior to Java 1.5, Iterator was used toprovide generic iteration for Collectionimplementations.


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Iterator

//example: collection of stringsIterator iter = collection.iterator();

while(iter.hasNext) {String s = (String) iter.next();// do stuff with s

}


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Algorithms

java.util.CollectionsUtility class where useful routines can befound.

SortingSearchingFinding Maximum, MinimumReversingShufflingmore...


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Java 1.5 Enhancements

GenericsFor-Each Loop

Autoboxing


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Generics

You can enforce type on the collection.

List list

= new ArrayList();

String s = list.get(5);// no need to cast!

list.add(new Integer(5));// will not compile


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For-Each Loop

Use the same loop construct for arraysand collections:

for(String s : collection) {System.out.println(s);

}


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Autoboxing

You can now use primitives in Collections

list.add(3);

map.put(4857, employee);


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Best Practices

Always use the Interface.Always use the Iterator (1.4) or the For-Each Loop (1.5).

MELJUN CORTES JAVA_Collections

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