Map Interfaces

The Map interface maps unique keys to values. A key is an object that you use to retrieve a value at a later date.
Architecture of Map interface:

Hashtable: Hashtable is similar to HashMap except it is synchronized.
import java.util.Hashtable; /** * * @author manojkumar */ public class HashtableExample { public static void main(String []args){ //Create String hashtable Object. Hashtable<String, String> hashtable=new Hashtable<String, String>(); hashtable.put("Sum", "67"); hashtable.put("Total", "654"); System.out.println("String, hashtable Contains :"+hashtable); //Create Integer hashtable Object. Hashtable<Integer, Integer> hashtableint=new Hashtable<Integer, Integer>(); hashtableint.put(1,2); hashtableint.put(3,4); System.out.println("Integer, hashtable Contains :"+hashtableint); } }
Output:         String, hashtable Contains :{Total=654, Sum=67}
                     Integer, hashtable Contains :{3=4, 1=2}  
LinkedHashMap: It is Hashtable and LinkedList implementation of  map interface. LinkedHashMap has a doublelinkedlist Running through all its elements.
import java.util.LinkedHashMap; public class LinkedHashMapExample { public static void main(String []args){ //Create LinkedHashMap Object. LinkedHashMap<String, Integer> linkedhashmap=new LinkedHashMap<String, Integer>(); linkedhashmap.put("Hi", 1); linkedhashmap.put("manoj", 2); linkedhashmap.put("welcom", 3); System.out.println("Put, LinkedHashMap Contains :"+linkedhashmap); linkedhashmap.remove("manoj"); System.out.println("Remove, LinkedHashMap Contains :"+linkedhashmap); } }
Output:                Put, LinkedHashMap Contains :{Hi=1, manoj=2, welcom=3}
                             Remove, LinkedHashMap Contains :{Hi=1, welcom=3}
HashMap: A HashMap is a Hashtable implementation of map interface, unlike HashMap it contains null keys and values. HashMap does not guarantee that the order of the objects will remain same over the time.
import java.util.HashMap; /** * * @author manojkumar */ public class HashMapExample { public static void main(String []args){ //Create HashMap Object. HashMap<String, Integer> hashmap=new HashMap<String, Integer>(); hashmap.put("Hi", 1); hashmap.put("manoj", 2); hashmap.put("welcom", 3); System.out.println("Put, HashMap Contains :"+hashmap); hashmap.remove("manoj"); System.out.println("Remove, HashMap Contains :"+hashmap); } }
Output:                Put, HashMap Contains :{Hi=1, welcom=3, manoj=2}
                             Remove, HashMap Contains :{Hi=1, welcom=3}
TreeMap: A TreeMap Provides red-block tree based implementation of map interface.
import java.util.TreeMap; /** * * @author manojkumar */ public class TreeMapExample { public static void main(String []args){ //Create TreeMap Object. TreeMap<String, Integer> treemap=new TreeMap<String, Integer>(); treemap.put("Hi", 1); treemap.put("manoj", 2); treemap.put("welcom", 3); System.out.println("Put, treeMap Contains :"+treemap); treemap.remove("manoj"); System.out.println("Remove, treeMap Contains :"+treemap); } }
Output:               Put, treeMap Contains :{Hi=1, manoj=2, welcom=3}
                            Remove, treeMap Contains :{Hi=1, welcom=3}