ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

What is Map in Java and there different implementations e.g. hashmap in Java

Updated on March 17, 2012

Map is common data structure and an important part of application programming , different language supports map in different way in this article we will see how Java supports Maps. For beginners Map is data structure which is used to put data as key value pair for quick retrieval. Map is derived from hashing technique and offers speedy retrieval of stored location known as bucket and based on efficiency of hashing technique can match array with consistent time for retrieval operation. Map allows two operations put and get, put is used to keep value into Map and get is used to take value from HashMap, sometime collision might happen when hashing technique finds same bucket position for various key elements. To resolve collision a linked list is kept in bucket are and every node of linked list stores data that is built of both value and key objects. Java Software is one of the preferred language because of its various capabilities such as platform independence, security and object oriented technique but except these main capability what java provides is full in built library for various mobile programming sought for and one of them are java collection API which provides HashMap, ArrayList, LinkedList and various different collection classes. In Java Collection is used to indicate those classes which store or store other objects. Java store its collection classes in java.util package and provides one interface called Map. Map describes basic possible operation in any kind of Map implementation for example get and put operation. In Java a map don't store any duplicate keys and every key can map to at most one value. Java supply many implementation of Map interface and those implementations are also present in java.util package. Some of most commonly Map implementations are IdentityHashMap, HashMap, and LinkedHashMap and HashMap in Java is the most popular of them after ArrayList in Java. These collection types are based on many data structure e.g. LinkedList, Array and Map. In this article we will discuss different collection classes based on HashMap data structure and Map interface.


The order of the map is the order in which the Iterator of the map's collection views returns their constituents. Iterator is an object which is used to retrieve objects from Collection within a loop. Some Map examples like the TreeMap maintains there order since they are derived from SortedMap and others, like HashMap doesn't maintains any order. To see more on How HashMap works in Java check on link. It’s imperative to understand that key object should implement equals and hashcode methods correctly in Java and caution great care must exercise if mutable elements are used as Map keys. Behavior of a map is uncertain if the value of an element is altered in a way which impact equals comparisons while the object is a key in map. IdentityHashMap implements Map interface with a hash table, uses reference-equality in place of object-equality while comparing keys (and values).


Couple of Map implementations also has restrictions on the keys and values they contain. For example some implementation doesn't keep null values and null keys and few have restrictions on the class of there keys. Insertion of wrong key or value throws unchecked exception , typically NullPointerException or ClassCastException for example TreeMap can't permit classes other than Type of there keys it intends you cannot put String and Double in TreeMap since they get compare to one another to allow sorted order and shall throw ClassCastException while comparing String and other class. Another important type which is based upon hashing and gives Map kind of functionality is Hashtable. Hashtable is present in java from JDK1.0 and don't extends Map interface rather than it implements Dictionary interface. Hashtable gives same functionality as HashMap but varies from HashMap in little respect you can look http://javarevisited.blogspot.com/2010/10/difference-between-hashmap-and.html here.

Comments

    0 of 8192 characters used
    Post Comment

    working

    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, hubpages.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://hubpages.com/privacy-policy#gdpr

    Show Details
    Necessary
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Features
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Marketing
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Statistics
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)