Java collections

AProperties object

is a persistent Hashtable object. Class Properties extends Hashtable.The Properties no-argument constructor creates an empty Properties table with no defaul tproperties. There is also an overloaded constructor that is passed a reference to a default Properties object containing default property values.

Interface List

is implemented by classes ArrayList, LinkedList and Vector. Class ArrayList is a resizable-array implementation of a List. A LinkedList is a linked list implementation of a List.

The classes and interfaces of the collections framework are in package

java.util.

Algorithm binarySearch

locates an Object in a sorted List.

Propertiesmethod getProperty

locates the value of the key specified as an argument.

Class Collections provides static methods for

manipulating collections. Many of the methods are implementations of polymorphic algorithms for searching, sorting and so on.

Maps

map keys to values and cannot contain duplicate keys. Maps differ from Sets in that Maps contain both keys and values, whereas Sets contain only values.

PriorityQueue,

one of the Queue implementations, orders elements by their natural ordering (i.e., the implementation of the compareTo method) or by a Comparator object that is supplied through the constructor.

A List is an

ordered Collection that can contain duplicate elements.

The Comparator interface

provides a means of sorting a Collection's elements in an order other than their natural order.

The Collections API

provides a set of public static methods for converting collections to unmodifiable versions. Unmodifiable wrappers throw UnsupportedOperationExceptions if attempts are made to modify the collection.

Algorithm shuffle

randomly orders the elements of a List

Method clear

removes elements from a List.

removeAllElements

removes every element from the Vector. Method removeElement At removes the element at the specified index.

Vector method remove

removes the first occurrence of its argument from the Vector. Method

pop

removes the top element of the stack.

Method load

restores the contents of the Properties object from the InputStream object pecified as the argument.

Collections method reverseOrder

returns a Comparator object that can be used with sort to sort elements of a collection in reverse order.

method get

returns a List element.

Vector method firstElement

returns a reference to the first element. Method lastElement returns a reference to the last element

Method peek

returns a reference to the top element without removing it.

HashMap method keySet

returns a set of the keys. Map methods size and isEmpty return the number of key-value pairs in the Map and a boolean indicating whether the Map is empty, respectively.

Method toArray

returns the contents of a collection as an array.

Algorithm reverse

reverses the elements of a List, fillsets every List element to a specified Object, and copy copies elements from one List into another

Method store

saves the contents of the Properties object to the OutputStream object specified as the first argument.

Algorithm sort

sorts the elements of a List.

Properties method setProperty

specifies the value associated with the key argument.

HashMaps

store elements in a hash table

TreeMaps

store elements in a tree.

Hashtables and HashMaps

store elements in hash tables, and TreeMaps store elements in trees.

Interface Collection

the root interface in the collection hierarchy from which interfaces Set and List are derived. Interface Collection contains bulk operations for adding, clearing, comparing and retaining objects in a collection. Interface Collection provides a method iterator for getting an Iterator.

HashMap

is a generic class that takes two type arguments. The first type argument specifies the type of key, and the second the type of value.

Class Arrays static methods for manipulating arrays,

including sort for sorting an array, binary Search for searching a sorted array, equals for comparing arrays and fill for placing items in an array.

Method insertElementAt

inserts an element at the specified position. Method set sets the element at a specific position.

A collection framework contains

Interfaces: These are abstract data types that represent collections. Thanks to interfaces, collections can be manipulated independently of the details of their representation Implementations: these are the concrete implementations of the collection interfaces. They are reusable data structures Algorithms: are the methods that perform useful computations such as searching, sorting on objects that implement collection interfaces. These algorithms are said to be polymorphic, meaning the same method can be used on many different implementations of the appropriate collection interface thereby being reusable.

classs Objectives

1. An understanding of the collection, list and set interfaces 2. An understanding of the queue interfaces 3. An understanding of the arraylist, hashset ,priorityqueue and treeset classes 4. An understanding of treemap and hashmap classes 5. Understanding of collection algorithms

what is a collection

A collection is an object that can hold references to other objects. The collection interfaces declare the operations that can be performed on each type of collection.

Method subList returns a view of a portion of a List.

Any changes made to this view are also made to the List.

Why use the java collections Framework?

Reduction of programming effort: Increasing program speed and quality: Facilitation of interoperability among unrelated APIs: Reduction in the effort needed to learn and use new APIs: Reduction in the effort need to design new APIs: Encourage software reuse:

whats is the java collection framework used for

The Java collections framework gives the programmer access to prepackaged data structures as well as to algorithms for manipulating them.

Arrays method asList returns

a List view of an array, which enables a program to manipulate the array as if it were a List. Any modifications made through the List view change the array, and any modifications to the array change the List view.

Queue,

a new collection interface introduced in Java SE 5, extends interface Collection and provides additional operations for inserting, removing and inspecting elements in a queue.

HashMap method put

adds a key and a value into a HashMap. Method get locates the value associated with the specified key. Method isEmpty determines whether the map is empty.

Vector method add

adds its argument to the end of the Vector.

Stack method push

adds its argument to the top of the stack.

Algorithms addAll

appends all the elements in an array to a collection, frequency calculates how many elements in the collection are equal to the specified element, and disjoint determines whether two collections have elements in common.

PriorityQueue operations

are offer to insert an element at the appropriate location based on priority order, poll to remove the highest-priority element of the priority queue(i.e., the head of the queue), peek to get a reference to the highest-priority element of the priorityqueue, clear to remove all elements in the priority queue and size to get the number of elements in the priority queue.

Synchronization wrappers

are provided for collections that can be accessed by multiple threads simultaneously.

Vector method contains

determines whether the Vector contains the searchKey specified as an argument. Vector method indexOf gets the index of the first location of its argument. The method returns -1 if the argument is not found in the Vector.

Vector method isEmpty

determines whether the Vector is empty. Methods size and capacity determine the number of elements currently in the Vector and the number of elements that can be stored in the Vector without allocating more memory, respectively.

Stack method empty

determines whether the stack is empty.

Class Vector manages

dynamically resizable arrays. At any time, a Vector contains a number of elements that is less than or equal to its capacity. If a Vector needs to grow, it grows by its capacity increment. If no capacity increment is specified, Java doubles the size of the Vector each time additional capacity is required. The default capacity is 10 elements.

Interface SortedMap

extends Map and represents a map that maintains its keys in sorted order.Class TreeMap implements SortedMap.

Interface SortedSet

extends Set and represents a set that maintains its elements in sorted order.Class TreeSet implements SortedSet.

Algorithms min and max

find the smallest and largest items in a collection.

Collections from the collections synchronized

framework are unsynchronized.

TreeSet method headSet

gets a view of a TreeSet that is less than a specified element. Method tailSet gets a view that is greater than or equal to a specified element. Any changes made to the view are made to the TreeSet.

Method size

gets the number of items in a List,

Iterator method

hasNext determines whether a Collection contains another element. Method next returns a reference to the next object in the Collection and advances the Iterator.

ASet

is a Collection that contains no duplicate elements. HashSet stores its elements in a hashtable. TreeSet stores its elements in a tree.