Java-7: CollectionsMasudul Haque

A collection — sometimes called a container — is simply an object that groups multiple elements into a single unit. Collections are used to store, retrieve, manipulate, and communicate aggregate data.

What is collection?

Data Structure Interface Implementation Algorithm Concurrency

Collection Framework

Jdk 1.0: Vector, Stack, Dictionary, Hashtable, Enumeration

Jdk 1.2: List, Set, Map, ArrayList, LinkedList, HashSet, TreeSet, HashMap, WeakHashMap

Jdk 1.4: RandomAccess, IdentityHashMap, LinkedHashMap

Jdk 1.5: Queue, java.util.concurrent Jdk 1.6: Deque, NavigableSet/Map Jdk 1.7: TransferQueue,

LinkedTransferQueue

History

Reduces programming effort. Increases programming speed and quality. Allows interoperability of unrelated data. Reduces learning effort. Reduces effort of to design new APIs Foster software reuse.

Collection Benefits

Collection

Collection Interface

List Interface

List Implementations

Indexed access Uses offset from memory address for fast

memory access In Java - fixed size memory block with VM-

level support

ArrayList

Dynamic structure made of pointers Easy to insert and delete new elements No indexed access

LinkedList

ArrayList vs LinkedList

Think of an example with ArrayList:

List<String> listA = new ArrayList<>(); listA.add("B"); listA.add("C"); listA.add("D"); listA.add("C");

for (String string : listA) { //Iteration if (string.equals("C")) { listA.remove("C"); //ConcurrentModificationExp } } System.out.println(listA);

CopyOnWriteArrayList

List<String> listA = new CopyOnWriteArrayList<>(); listA.add("B"); listA.add("C"); listA.add("D"); listA.add("C");

for (String string : listA) { if (string.equals("C")) { listA.remove("C"); } } System.out.println(listA);

CopyOnWriteArrayList

Thread safe. Never throws ConcurrentModifi- cationEception.

Copy-on-write operation. Snapshot iterator.

CopyOnWriteArrayList

Data Structure Sorting Iterator Null

Support?

ArrayList Array No Fail-fast Yes

LinkedLIst Linked list No Fail-fast Yes

CopyOnWriteArrayList Array No Snapshot Yes

List Comparison

add remove get contain

ArrayList O(1) O(n) O(1) O(n)

LinkedLIst O(1) O(1) O(n) O(n)

CopyOnWriteArrayList O(n) O(n) O(1) O(n)

List Performance Comparison

Fail-fast - work on live data, but become invalid when live data is modified

Weakly consistent - work on live data, safe, reflect updates and deletes, but not inserts

Snapshot - work on a snapshot of the live data, fast, safe, but possibly stale

Iterator

Set Interface

first() : E last() : E headSet(E toElem) : SortedSet<E> subSet(E fromElem, E toElem) :

SortedSet<E> tailSet(E fromElem) : SortedSet<E> comparator() : Comparator<? super E>

Sorted Set

pollFirst() : E pollLast() : E

subSet(E from, boolean inclusive, E to, boolean inclusive) : NavigableSet<E>

headSet(E to, boolean inclusive) : NavigableSet<E> tailSet(E from, boolean inclusive) : NavigableSet<E>

ceiling(E e) : E floor(E e) : E higher(E e) : E lower(E e) : E

descendingSet() : NavigableSet<E> descendingIterator() : Iterator<E>

NavigableSet

Set Implementation

Data Structure Sorting Iterator Nulls?

HashSet Hash table No Fail-fast Yes

LinkedHash Set

Hash table+ Linked list

Insertion order Fail-fast Yes

EnumSet Bit Vector Natural order Weekly Consistent No

TreeSet Red-black tree Sorted Fail-fast Depends

CopyOnWriteArraySet Array No Snapshot Yes

ConcurrentSkipListSet Skip list Sorted Weekly

Consistent No

Comparing Set

Series of linked list Reasonably fast search add and remove Lock free implementation

Skip Lists

add contains next

HashSet O(1) O(1) O(h/n)

LinkedHash Set O(1) O(1) O(1)

EnumSet O(1) O(1) O(1)

TreeSet O(log n) O(log n) O(log n)

CopyOnWriteArraySet O(n) O(n) O(1)

ConcurrentSkipListSet O(log n) O(log n) O(1)

Comparing Set Performance

Queues & Deques

Throws exception Returns special value

Insert add(e) offer(e)

Remove remove() poll()

Examine element() peek()

Queue Method

Throws exception

Special value Blocks Time out

Insert add(e) offer(e) put(e) offer(e,time, unit)

Remove remove() poll() take() poll(time, unit)

Examine element() peek() Not applicable

Not applicable

BlockingQueue Method

Queue Implementation

Balanced binary tree Root is always highest priority Inserts and removes cause re-balancing

Data Structure: PriorityQueue

Head:Throws exception

Head: Special value

Tail: Throws exception

Tail: Special value

Insert addFirst(e)Stack: push

offerFirst(e) addLast(e)Queue: add

offerLast(e) Queue: offer

RemoveremoveFirst()Queue: remove

Stack:pop

pollFirst() Queue: poll

removeLast() pollLast()

Examine getFirst() Queue: element

peekFirst()Queue:peek Stack:peek

getLast() peekLast()

Deque Method

Head Throws exception Special value Blocks Time out

Insert addFirst(e)Stack: push

offerFirst(e) putFirst(e)Queue: add

offerFirst(e, time,unit) Queue: offer

Remove removeFirst()Queue: remove

pollFirst() Queue: poll

takeFirst() pollFirst(e, time,unit)

Examine getFirst() Queue: element

peekFirst()Queue:peek Stack:peek

BlockingDeque Method

Tail Throws exception Special value Blocks Time out

Insert addLast(e)Stack: push

offerLast(e) putLast(e)Queue: put

offerLast(e, time, unit) Queue: offer

RemoveremoveLast()Queue: remove

Stack:pop

pollLast() Queue: poll

takeLast() pollLast(e, time, unit)

Examine getLast() Queue: element

peekLast()Queue:peek Stack:peek

Deque Implementation

Comparing Queue Implementation

Queue Performance

Producers wait for consumers to receive elements. Useful for message passing. Similar to a broader version of SynchronousQueue.

hasWaitingConsumer() : booleangetWaitingConsumerCount() : inttransfer(E e)tryTransfer(E e) : booleantryTransfer(E e, long timeout, TimeUnit unit) : boolean

TranserQueue

Map Interface

put(E key, V value) : VputAll(Map<? extends K, ? extends V> m)remove(Object key) : Vclear()containsKey(Object key) : booleancontainsValue(Object value) : booleanisEmpty() : booleansize() : intget(Object key) : VentrySet() : Set<Map.Entry<K,V>>keySet() : Set<K>values() : Collection<V>

Map Interface

firstKey() : KlastKey() : KheadMap(K to) : SortedMap<K, V>subMap(K from, K to) : SortedMap<K, V>tailMap(K from) : SortedMap<K, V>comparator() : Comparator<? super K>

Sorted Map

firstEntry() : Map.Entry<K,V>lastEntry() : Map.Entry<K,V>ceilingEntry(K key) : Map.Entry<K,V>ceilingKey(K key) : KfloorEntry(K key) : Map.Entry<K,V>floorKey(K key) : KhigherEntry(K key) : Map.Entry<K,V>higherKey(K key) : KlowerEntry() : Map.Entry<K,V>lowerEntry(K key) : KnavigableKeySet() : NavigableSet<K>pollFirstEntry() : Map.Entry<K,V>pollLastEntry() : Map.Entry<K,V>headMap(K to, boolean inclusive) : NavigableMap<K,V>subMap(K from, boolean fromInc, K to, boolean toInc) : NavigableMap<K,V>tailMap(K from, boolean inclusive) : NavigableMap<K,V>descendingKeySet() : NavigableSet<K>descendingMap() : NavigableMap<K,V>

NavigableMap

putIfAbsent(K key, V value) : Vremove(Object key, Object value) : booleanreplace(K key, V value) : Vreplace(K key, V oldValue, V newValue) : boolean

ConcurrentMap

Map Implementation

Comparing Map Implementation

Map Performance

Collections Class