Important Note:<\/strong><\/span>\u00a0HashMap allows null key and null value in it, but with a restriction that there can be only one null key and multiple null values.<\/p>\n HashMap Class extends AbstractMap Class and that Implements Map Interface as shown in\u00a0 figure 1.<\/p>\n Let us discuss Hash map with the help of following\u00a0programs.<\/p>\n In this\u00a0program we have created object of HashMap Class, added key value pairs using put method, and displayed it using getKey and getValue methods , as shown\u00a0below<\/p>\n Output<\/strong><\/p>\n Description:<\/strong><\/p>\n for(Map.Entry map\u00a0 :\u00a0 HashMap.entrySet())<\/strong><\/p>\n In this for loop we have used method entrySet(), which returns a Set view of the mappings contained in the HashMap object and the Map.Entry is an Interface that enables you to work with a map entry easily by which key-value pairs are retrieved one by one, and are displayed in next step.<\/p>\n System.out<\/em>.println(map.getKey()+” “+map.getValue());<\/strong><\/p>\n First is\u00a0 getKey() , which as name suggest retrieves the key and secondly getValue() method that retrieves the value corresponding to the given key.<\/p>\n HashMap does not allow Entry with duplicate key, it overlaps old value with new one. Below program helps you understand this.<\/p>\n In this program we have created object of HashMap Class and added key value pairs, one with duplicate key, as shown in the following program<\/p>\n Output:<\/strong><\/p>\n Conclusion:<\/strong>\u00a0From output it is clear that HashMap does not allow Entry with duplicate key, it overlaps old value with new one, as shown in the output.<\/p>\n Description of Program:<\/strong><\/p>\n HashMap allows Entry with duplicate value\u00a0but having unique key.<\/p>\n In this program we have created object of HashMap Class and added key value pairs, one with duplicate value, as shown in the following program<\/p>\n Output:<\/strong><\/p>\n Conclusion:<\/strong>\u00a0From output it is clear that HashMap allows Entry with duplicate value.<\/p>\n Description:<\/strong><\/p>\n HashMap is a class that implements Map Interface and Extends AbstractMap class.\u00a0\u00a0It is generally denoted as HashMap <key, value> or HashMap <K,V>.<\/p>\n Let us discuss HashMap methods one by one with Examples in Java.<\/p>\n 1. Object put(Object key, Object value):<\/strong><\/span><\/p>\n This method adds the key value pair to the HashMap object, as shown in the following program:<\/p>\n Output:<\/strong><\/p>\n 2. int size():<\/strong><\/span><\/p>\n This method returns the size of the HashMap as shown in the following program:<\/p>\n Output:<\/strong><\/p>\n 3. void clear():<\/strong><\/span><\/p>\n This method clears all the key value pairs in the HashMap, as shown in the following program:<\/p>\n Output:<\/strong><\/p>\n Read all HashMap Methods in JAVA<\/a><\/p>\n HashMap is a type of Collection, that stores our data in a pair such that each element has a key associated with it. The pair of key and value is often known as Entry and these entries can have only unique keys. HashMap is a class that implements Map Interface and Extends AbstractMap class which … Continue reading HashMap Tutorial In Java with Example<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"open","ping_status":"closed","template":"home.php","meta":{"footnotes":""},"class_list":["post-673","page","type-page","status-publish","hentry"],"psp_head":"
\nHierarchy of HashMap Class<\/strong><\/h4>\n
![\"hierarchy](\"\/java\/wp-content\/uploads\/2016\/02\/hierarchy-of-hashmap.png\")
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\n\u00a0Examples of HashMap class<\/strong><\/h4>\n
import java.util.*;\r\n\r\npublic class HashMapDemoClass{\r\n\r\npublic static void main(String args[]){\r\n\r\n\/\/Step 1: Defing object of HashMap Class\r\n\r\nHashMap<Integer,String> HashMap=new HashMap<Integer,String>();\r\n\r\n\/\/Step 2: Adding Key Value pair\r\n\r\nHashMap.put(1001,\"India\");\r\n\r\nHashMap.put(1002,\"Canada\");\r\n\r\nHashMap.put(1003,\"Australia\");\r\n\r\n\/\/Step 3: Displaying key value pairs using for loop\r\n\r\nfor(Map.Entry map\u00a0 :\u00a0 HashMap.entrySet() )\r\n\r\n{\r\n\r\n\/\/Step 4: Using getKey and getValue methods to retrieve key and corresponding value\r\n\r\nSystem.out<\/em>.println(map.getKey()+\" \"+map.getValue());\r\n\r\n}\r\n}\r\n}\r\n<\/pre>\n1001 India\r\n\r\n1002 Canada\r\n\r\n1003 Australia\r\n<\/pre>\n
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\nAdding Entry with Duplicate Key in HashMap<\/strong><\/h4>\n
import java.util.*;\r\npublic class HashMapDemoClass{\r\npublic static void main(String args[]){\r\n\r\n\/\/Step 1: Defining object of HashMap Class\r\nHashMap<Integer,String> HashMap=new HashMap<Integer,String>();\r\n\r\n\/\/Step 2: Adding Key Value pair\r\n\r\nHashMap.put(1001,\"India\");\r\n\r\nHashMap.put(1002,\"Canada\");\r\n\r\nHashMap.put(1003,\"Australia\");\r\n\r\n\/\/Step 3: Displaying key value pairs using for loop\r\n\r\nfor(Map.Entry map\u00a0 :\u00a0 HashMap.entrySet() )\r\n\r\n{\r\n\r\n\/\/Step 4: Using getKey and getValue methods to retrieve key and corresponding value\r\n\r\nSystem.out.println(map.getKey()+\" \"+map.getValue());\r\n\r\n}\r\n\r\n\/\/Step 5: Adding element with duplicate key\r\n\r\nHashMap.put(1003,\"Nepal\");\r\n\r\n\u00a0\r\n\/\/Step 6: Displaying Elemnets\r\n\r\nSystem.out.println(\"Entries after adding element with Duplicate Key\");\r\n\r\nfor(Map.Entry map\u00a0 :\u00a0 HashMap.entrySet() )\r\n\r\n{\r\n\r\nSystem.out.println(map.getKey()+\" \"+map.getValue());\r\n}\r\n}\r\n}\r\n\r\n<\/pre>\n1001 India\r\n\r\n1002 Canada\r\n\r\n1003 Australia\r\n\r\nEntries after adding element with Duplicate Key\r\n\r\n1001 India\r\n\r\n1002 Canada\r\n\r\n1003 Nepal\r\n<\/pre>\n
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\nAdding Entry with Duplicate Value in HashMap<\/strong><\/h4>\n
import java.util.*;\r\npublic class HashMapDemoClass{\r\npublic static void main(String args[]){\r\n\r\n\/\/Step 1: Defing object of HashMap Class\r\n\r\nHashMap<Integer,String> HashMap=new HashMap<Integer,String>();\r\n\u00a0\r\n\r\n\/\/Step 2: Adding Key Value pair\r\n\r\nHashMap.put(1001,\"India\");\r\n\r\nHashMap.put(1002,\"Canada\");\r\n\r\nHashMap.put(1003,\"Australia\");\r\n\r\n\/\/Step 3: Displaying key value pairs using for loop\r\n\r\nfor(Map.Entry map\u00a0 :\u00a0 HashMap.entrySet() )\r\n\r\n{\r\n\r\n\/\/Step 4: Using getKey and getValue methods to retrieve key and corresponding value\r\n\r\nSystem.out.println(map.getKey()+\" \"+map.getValue());\r\n\r\n}\r\n\r\n\/\/Step 5: Adding element with duplicate value\r\n\r\nHashMap.put(1004,\"India\");\r\n\r\n\/\/Step 6: Displaying Elemnets\r\n\r\nSystem.out.println(\"Entries after adding element with Duplicate Value\");\r\n\r\nfor(Map.Entry map\u00a0 :\u00a0 HashMap.entrySet() )\r\n\r\n{\r\n\r\nSystem.out.println(map.getKey()+\" \"+map.getValue());\r\n\r\n}\r\n\r\n}\r\n\r\n}\r\n<\/pre>\n1001 India\r\n\r\n1002 Canada\r\n\r\n1003 Australia\r\n\r\nEntries after adding element with Duplicate Value\r\n\r\n1001 India\r\n\r\n1002 Canada\r\n\r\n1003 Australia\r\n\r\n1004 India\r\n<\/pre>\n
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\nHashMap Methods in JAVA:<\/strong><\/h4>\n
import java.util.*;\r\n\r\npublic class HashMapDemoClass \r\n{\r\n\r\n public static void main(String args[]) {\r\n\r\n\/\/ create a hashmap\r\n\r\n HashMap hashmapobj = new HashMap();\r\n\r\n\/\/ using Object put(Object key, Object value) method\r\n\r\n hashmapobj.put(1001, \"I\");\r\n\r\n hashmapobj.put(1002, \"Love\");\r\n\r\n hashmapobj.put(1003, \"Java\");\r\n\r\n\/\/printing the hashmap\r\n\r\n System.out.println(\" All the key value pairs \" + hashmapobj);\r\n\r\n }\r\n\r\n}<\/pre>\nAll the key value pairs {1001=I, 1002=Love, 1003=Java}<\/pre>\npackage com.test;\r\nimport java.util.*;\r\n\r\npublic class HashMapDemoClass \r\n{\r\n\r\n public static void main(String args[]) {\r\n\r\n \/\/ create a hashmap\r\n\r\n HashMap hashmapobj = new HashMap();\r\n\r\n hashmapobj.put(1001, \"I\");\r\n\r\n hashmapobj.put(1002, \"Love\");\r\n\r\n hashmapobj.put(1003, \"Java\");\r\n\r\n \/\/using size() method\r\n\r\n System.out.println(\" Size of hashmap is \" + hashmapobj.size());\r\n\r\n }\r\n\r\n}<\/pre>\nSize of hashmap is 3<\/pre>\n
import java.util.*;\r\n\r\npublic class HashMapDemoClass \r\n{\r\n\r\n public static void main(String args[]) {\r\n\r\n \/\/ create a hashmap\r\n\r\n HashMap hashmapobj = new HashMap();\r\n\r\n hashmapobj.put(1001, \"I\");\r\n\r\n hashmapobj.put(1002, \"Love\");\r\n\r\n hashmapobj.put(1003, \"Java\");\r\n\r\n \/\/using size() method\r\n\r\n System.out.println(\" Size of hashmap is \" + hashmapobj.size());\r\n\r\n \/\/using clear() method\r\n\r\n hashmapobj.clear();\r\n\r\n \/\/using size() method\u00a0 after clearing the hashmap\r\n\r\n System.out.println(\" Size of hashmap after clearing is \" + hashmapobj.size());\r\n\r\n }\r\n\r\n}<\/pre>\nSize of hashmap is 3\r\n\r\nSize of hashmap after clearing is 0<\/pre>\n
\nImportant Points About HashMap<\/strong><\/h4>\n
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\nHashMap Quick Revision Points<\/strong><\/h4>\n
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