HashMap is a one-to-one relationship between one object and other object. Let us take a real life example of hash map for better understanding of this concept:<\/p>\n
Let’s assume you want to open\u00a0your email account. But to do that\u00a0you’re taken to a login screen where you type in your username and password. When the combination is correct only then your email account open.<\/p>\n
A hashmap works in a similar way. You have to give it an appropriate input so you can get the proper output. Each input is mapped to exactly one output. In our previous example, one combination of username and password produces exactly one email account.<\/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 all the 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><\/span><\/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><\/span><\/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><\/span><\/p>\n 4. Object clone():<\/strong><\/span><\/p>\n This method returns the exact copy of the HashMap, as shown in the following program:<\/p>\n Output:<\/strong><\/span><\/p>\n 5. boolean containsKey(Object key):<\/strong><\/span><\/p>\n This method checks the presence of specified\u00a0 key in the HashMap, it will return true if the key is present and false if the mentioned key is not present, as shown in the following program:<\/p>\n Output:<\/strong><\/span><\/p>\n 6. boolean containsValue(Object value):<\/strong><\/span><\/p>\n This method checks the presence of specified value in the HashMap, it will return true if the value is present and false if the mentioned value is not present, as shown in the following program:<\/p>\n Output:<\/strong><\/span><\/p>\n 7. Set entrySet():<\/strong><\/span><\/p>\n This method returns a Set view of the mappings contained in the HashMap, as shown in the following program:<\/p>\n Output:<\/strong><\/span><\/p>\n 8. Object get(Object key):<\/strong><\/span><\/p>\n This method returns the value corresponding to the specified key, as shown in the following program:<\/p>\n Output:<\/strong><\/span><\/p>\n 9.boolean isEmpty():<\/strong><\/span><\/p>\n This method as the name suggests checks whether the HashMap is empty or not, It will return true if it is empty, or false if it is not empty, as shown in the following program:<\/p>\n Output:<\/strong><\/span><\/p>\n 10. Set keySet():<\/strong><\/span><\/p>\n This method returns a Set view of the keys contained in the HashMap ,as shown in the following program:<\/p>\n Output:<\/strong><\/span><\/p>\n 11. putAll(Map m):<\/strong><\/span><\/p>\n This method copies all the key value pair form one hashmap to another , as shown in the following program:<\/p>\n Output:<\/strong><\/span><\/p>\n 12. Object remove(Object key):<\/strong><\/span><\/p>\n This method as the name specifies removes the key value pair, corresponding to the mentioned key in the argument list, as shown in the following program:<\/p>\n Output:<\/strong><\/span><\/p>\n 13. Collection values():<\/strong><\/span><\/p>\n This method returns the collection of all the values in the hashmap, as shown in the following program:<\/p>\n Output:<\/strong><\/span><\/p>\n HashMap is a one-to-one relationship between one object and other object. Let us take a real life example of hash map for better understanding of this concept: Let’s assume you want to open\u00a0your email account. But to do that\u00a0you’re taken to a login screen where you type in your username and password. When the combination … Continue reading HashMap Methods Tutorials in Java With Examples<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1,77],"tags":[],"class_list":["post-670","post","type-post","status-publish","format-standard","hentry","category-archieve","category-java-collections"],"psp_head":"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
package 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 hashmapobj1 = new HashMap();\r\n\r\n hashmapobj1.put(1001, \"I\");\r\n\r\n hashmapobj1.put(1002, \"Love\");\r\n\r\n hashmapobj1.put(1003, \"Java\");\r\n\r\n \/\/Creating a new hashmap\r\n\r\n HashMap hashmapobj2 = new HashMap();\r\n\r\n \/\/Using clone method\r\n\r\n hashmapobj2=(HashMap)hashmapobj1.clone();\r\n\r\n System.out.println(\"Cloned 2nd Map: \" + hashmapobj2);\r\n\r\n }\r\n\r\n}<\/pre>\nCloned 2nd Map: {1001=I, 1002=Love, 1003=Java}<\/pre>\npackage com.test;\r\n\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 hashmapobj1 = new HashMap();\r\n\r\n hashmapobj1.put(1001, \"I\");\r\n\r\n hashmapobj1.put(1002, \"Love\");\r\n\r\n hashmapobj1.put(1003, \"Java\");\r\n\r\n \/\/ check existence of key 1002\r\n\r\n System.out.println(\"Check if key 1002 exists: \" + hashmapobj1.containsKey(1002));\r\n\r\n \/\/ check existence of key 1000\r\n\r\n System.out.println(\"Check if key 1000 exists: \" + hashmapobj1.containsKey(1000));\r\n\r\n }\r\n\r\n}<\/pre>\nCheck if key 1002 exists: true\r\n\r\nCheck if key 1000 exists: false<\/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 hashmapobj1 = new HashMap();\r\n\r\n hashmapobj1.put(1001, \"I\");\r\n\r\n hashmapobj1.put(1002, \"Love\");\r\n\r\n hashmapobj1.put(1003, \"Java\");\r\n\r\n \/\/ check existence of value 'I'\r\n\r\n System.out.println(\"Check if value 'I' exists: \" +\u00a0 hashmapobj1.containsValue(\"I\"));\r\n\r\n\/\/ check existence of value 'India'\r\n\r\n System.out.println(\"Check if value 'India' exists: \" +\u00a0 hashmapobj1.containsValue(\"India\"));\r\n\r\n }\r\n\r\n}<\/pre>\nCheck if value 'I' exists: true\r\n\r\nCheck if value 'India' exists: false<\/pre>\n
package com.test;\r\n\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 hashmapobj1 = new HashMap();\r\n\r\n hashmapobj1.put(1001, \"I\");\r\n\r\n hashmapobj1.put(1002, \"Love\");\r\n\r\n hashmapobj1.put(1003, \"Java\");\r\n\r\n \/\/ create set of hashmap\r\n\r\n Set set=hashmapobj1.entrySet();\r\n\r\n System.out.println(\"Set values: \" + set);\r\n\r\n }\r\n\r\n}<\/pre>\nSet values: [1001=I, 1002=Love, 1003=Java]<\/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 hashmapobj1 = new HashMap();\r\n\r\n hashmapobj1.put(1001, \"I\");\r\n\r\n hashmapobj1.put(1002, \"Love\");\r\n\r\n hashmapobj1.put(1003, \"Java\");\r\n\r\n \/\/ get value of key 1003\r\n\r\n String str=(String)hashmapobj1.get(1003);\r\n\r\n System.out.println(\"Value for key 1003 is: \" + str);\r\n\r\n }\r\n\r\n}<\/pre>\nValue for key 1003 is: Java<\/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 hashmapobj1 = new HashMap();\r\n\r\n hashmapobj1.put(1001, \"I\");\r\n\r\n hashmapobj1.put(1002, \"Love\");\r\n\r\n hashmapobj1.put(1003, \"Java\");\r\n\r\n \/\/ check if the map is empty or not\r\n\r\n System.out.println(\" Hashmap is empty??\" + hashmapobj1.isEmpty());\r\n\r\n }\r\n\r\n}<\/pre>\nHashmap is empty??false<\/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 hashmapobj1 = new HashMap();\r\n\r\n hashmapobj1.put(1001, \"I\");\r\n\r\n hashmapobj1.put(1002, \"Love\");\r\n\r\n hashmapobj1.put(1003, \"Java\");\r\n\r\n \/\/ seting the keyset\r\n\r\n Set keyset=hashmapobj1.keySet();\r\n\r\n \/\/ check key set values\r\n\r\n System.out.println(\"Key values are: \" + keyset);\r\n\r\n }\r\n\r\n}\r\n<\/pre>\nKey values are: [1001, 1002, 1003]<\/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 hashmapobj1 = new HashMap();\r\n\r\n hashmapobj1.put(1001, \"I\");\r\n\r\n hashmapobj1.put(1002, \"Love\");\r\n\r\n hashmapobj1.put(1003, \"Java\");\r\n\r\n System.out.println(\"Values in newmap1: \"+ hashmapobj1);\r\n\r\n HashMap hashmapobj2 = new HashMap();\r\n\r\n \/\/ put all values in newmap2\r\n\r\n hashmapobj2.putAll(hashmapobj1);\r\n\r\n System.out.println(\"Values in hashmapobj2: \"+ hashmapobj2);\r\n\r\n }\r\n\r\n}<\/pre>\nValues in newmap1: {1001=I, 1002=Love, 1003=Java}\r\n\r\nValues in hashmapobj2: {1001=I, 1002=Love, 1003=Java}<\/pre>\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 hashmapobj1 = new HashMap();\r\n\r\n hashmapobj1.put(1001, \"I\");\r\n\r\n hashmapobj1.put(1002, \"Love\");\r\n\r\n hashmapobj1.put(1003, \"Java\");\r\n System.out.println(\"hashmap before\u00a0 using remove method: \"+ hashmapobj1);\r\n\r\n \/\/ remove value for key 1002\r\n\r\n hashmapobj1.remove(1002);\r\n\r\n System.out.println(\"hashmap after\u00a0 using remove method: \"+ hashmapobj1);\r\n\r\n }\r\n\r\n}<\/pre>\nhashmap before\u00a0 using remove method: {1001=I, 1002=Love, 1003=Java}\r\n\r\nhashmap after\u00a0 using remove method: {1001=I, 1003=Java}<\/pre>\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 hashmapobj1 = new HashMap();\r\n\r\n hashmapobj1.put(1001, \"I\");\r\n\r\n hashmapobj1.put(1002, \"Love\");\r\n\r\n hashmapobj1.put(1003, \"Java\");\r\n\r\n System.out.println(\"collection view of this hashmap is \"+ hashmapobj1.values());\r\n\r\n }\r\n\r\n}<\/pre>\ncollection view of this hashmap is [I, Love, Java]<\/pre>\n","protected":false},"excerpt":{"rendered":"