The HashMap class uses a hashtable to complete the Map interface. This allows the execution time of key operations, for instance, get( ) and put( ). A HashMap contains values in perspective of the key and amplifies AbstractMap class, includes exceptional components. Following is the syntax declaration for java.util HashMap Class. [java] public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable [/java] The Cloneable interface portrays no people. It is used to demonstrate that a class allows a bitwise copy of an example to be made. The Serializable interface is used to check java classes so that examples of the classes will get limit.

Following is an architecture of HashMap Class. TThe components of Map interface are the segments should be secured in key/esteem sets. Outline invalid values likewise both as key and values. Copy qualities are not permitted by Map.

Following are the constructors of java.util HashMap Class.

Following are the basic and regular using methods of java.util HashMap Class.

Following is the syntax declaration of the method. [java]public Collection<V> values()[/java] DemoHashMap.java [java] package com.SPlessons; import java.util.*; public class DemoHashMao { public static void main(String args[]) { // create hash map HashMap newmap = new HashMap(); // populate hash map newmap.put(1, "SPLessons"); newmap.put(2, "Start Coding"); newmap.put(3, "Stop Thinking"); // checking collection view of the map System.out.println("Collection view is: "+ newmap.values()); } } [/java] The put() strategy is utilized to relate the value with the key in the map. Output: Now compile the code result will be as follows. [java] Collection view is: [SPLessons, Start Coding, Stop Thinking] [/java]

Following is the syntax declaration of the method. [java]public Set<K> keySet()[/java] DemoHashMap.java [java] package com.SPlessons; import java.util.*; public class DemoHashMao { public static void main(String args[]) { // create hash map HashMap newmap = new HashMap(); // populate hash map newmap.put(1, "SPLessons"); newmap.put(2, "Start Coding"); newmap.put(3, "Stop Thinking"); // get keyset value from map Set keyset=newmap.keySet(); // check key set values System.out.println("Key set values are: " + keyset); } } [/java] The put() strategy is utilized to relate the value with the key in the map. By using keyset() method values of the map will be returned. Output: Now compile the code result will be as follows. [java] Key set values are: [1, 2, 3] [/java]

Following is the syntax declaration of the method. [java]public void clear()[/java] DemoHashMap.java [java] package com.SPlessons; import java.util.*; public class DemoHashMao { public static void main(String args[]) { // create hash map HashMap newmap = new HashMap(); // populate hash map newmap.put(1, "SPLessons"); newmap.put(2, "Start Coding"); newmap.put(3, "Stop Thinking"); System.out.println("First map elements: " + newmap); // clear hash map newmap.clear(); System.out.println("Map elements after clear: " + newmap); } } [/java] In the above example, all the mapping data is going to remove after using clear() method. Output: Now compile the code result will be as follows. [java] Initial map elements: {1=SPLessons, 2=Start Coding, 3=Stop Thinking} Map elements after clear: {} [/java]

Following is the syntax declaration of the method. [java]public Object clone()[/java] DemoHashMap.java [java] package com.SPlessons; import java.util.*; public class DemoHashMao { public static void main(String args[]) { // create two hash maps HashMap newmap1 = new HashMap(); HashMap newmap2 = new HashMap(); // populate hash map newmap1.put(1, "SPLessons"); newmap1.put(2, "Start Coding"); newmap1.put(3, "Stop Thinking"); // clone 1st map newmap2=(HashMap)newmap1.clone(); System.out.println("1st Map: " + newmap1); System.out.println("Cloned 2nd Map: " + newmap2); } } [/java] The clone() is a technique in the Java programming dialect for object duplication. In Java, objects are controlled through reference variables. Output: Now compile the code result will be as follows. [java] 1st Map: {1=SPLessons, 2=Start Coding, 3=Stop Thinking} Cloned 2nd Map: {1=SPLessons, 2=Start Coding, 3=Stop Thinking} [/java]

• The HashMap Class maintains no order.
• The HashMap Class may have multiple null values and single null value.
• The HashMap extends AbstractMap and AbstractMap implements Map interface.