{"id":1064,"date":"2016-03-09T07:33:14","date_gmt":"2016-03-09T07:33:14","guid":{"rendered":"http:\/\/abhiandroid.com\/java\/?page_id=1064"},"modified":"2018-06-05T06:31:13","modified_gmt":"2018-06-05T06:31:13","slug":"hashset","status":"publish","type":"page","link":"https:\/\/abhiandroid.com\/java\/hashset","title":{"rendered":"Hashset Tutorial In Java With Example"},"content":{"rendered":"

Hashset is a type of Java Collection that implements the Set Interface and extends AbstractSet Interface. As HashSet is an implementation of Set Interface, it do not allow duplicate values to be stored, But it can store null elements. Also it does not maintain insertion order.<\/p>\n

HashSet uses Hash table for storing the data. Hash table internally uses a phenomena known as hashing, In hashing a unique key is generated automatically called Hash code, which is mapped as the index of the elements in the hashset.<\/p>\n

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Hierarchy of HashSet class<\/strong><\/h4>\n

HashSet Class extends AbstractSet Class and implements Set Interface, Set Interface further extends Collection Interface and Iterable Interface, as shown in figure 1.<\/p>\n

Dotted Arrow shows implementation and Bold arrow shows Extending a Class.<\/p>\n

\"Hierarchy<\/center><\/p>\n
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HashSet Methods\u00a0in JAVA<\/strong><\/h4>\n

Let us discuss all the HashSet\u00a0methods one by one with Examples in Java.<\/p>\n

1. boolean add(Object o)<\/strong><\/span><\/p>\n

This methods adds the value in the hashSet, only if the element to be added is not present in existing Set, as shown in the following program.<\/p>\n

import java.util.*;\r\n\r\npublic class HashSetDemo{\r\n\r\npublic static void main(String args[]){\r\n\r\nHashSet <String> hashSetObject = new HashSet <String>();\r\n\r\n\/\/Calling add() mehthod\r\n\r\nhashSetObject.add(\"I\");\r\n\r\nhashSetObject.add(\"Love\");\r\n\r\nhashSetObject.add(\"Java\");\r\n\r\nhashSetObject.add(\"Java\");\r\n\r\nhashSetObject.add(\"I\");\r\n\r\nSystem.out<\/em>.println(\"values in HashSet object \"+ hashSetObject);\r\n}\r\n}\r\n<\/pre>\n
Output:<\/strong><\/span><\/p>\n
values in HashSet clone object [Java, Love, I]\r\n<\/pre>\n
In Output, We can see that we are not getting repeated values.<\/p>\n
2. void clear()<\/strong><\/span><\/p>\n
This method as the name suggests remove all the elements from the set, as shown in the following program<\/p>\n
import java.util.*;\r\n\r\npublic class HashSetDemo{\r\n\r\npublic static void main(String args[]){\r\n\r\nHashSet <String> hashSetObject = new HashSet <String>();\r\n\r\nhashSetObject.add(\"I\");\r\n\r\nhashSetObject.add(\"Love\");\r\n\r\nhashSetObject.add(\"Java\");\r\n\r\nSystem.out<\/em>.println(\"values in HashSet object \"+ hashSetObject);\r\n\r\n\/\/Calling clear() mehthod\r\n\r\nhashSetObject.clear();\r\n\r\nSystem.out<\/em>.println(\"values in HashSet object After using Clear method\"+ hashSetObject);\r\n}\r\n}\u00a0\r\n<\/pre>\n
Output:<\/strong><\/span><\/p>\n
values in HashSet object [Java, Love, I]\r\n\r\nvalues in HashSet object After using Clear method[]\r\n<\/pre>\n
3. Object clone()<\/strong><\/span><\/p>\n
This method returns the exact same copy of the hashSet object, as shown in the following program<\/p>\n
import java.util.*;\r\n\r\npublic class HashSetDemo{\r\n\r\npublic static void main(String args[]){\r\n\r\nHashSet <String> hashSetObject1 = new HashSet <String>();\r\n\r\nHashSet <String> hashSetObject2 = new HashSet <String>();\r\n\r\nhashSetObject1.add(\"I\");\r\n\r\nhashSetObject1.add(\"Love\");\r\n\r\nhashSetObject1.add(\"Java\");\r\n\r\nhashSetObject2= (HashSet) hashSetObject1.clone();\r\n\r\nSystem.out<\/em>.println(\"values in HashSet clone object \"+ \u00a0\u00a0hashSetObject2);\r\n}\r\n}\r\n<\/pre>\n
Output:<\/strong><\/span><\/p>\n
values in HashSet clone object [Java, I, Love]\u00a0<\/u><\/strong>\r\n<\/pre>\n
4. boolean contains(Object o)<\/strong><\/span><\/p>\n
This method returns true if the calling hashset object contains the specific element as given in the argument list, otherwise it returns false, as shown in the following program.<\/p>\n
import java.util.*;\r\n\r\npublic class HashSetDemo{\r\n\r\npublic static void main(String args[]){\r\n\r\nHashSet <String> hashSetObject = new HashSet <String>();\r\n\r\nhashSetObject.add(\"I\");\r\n\r\nhashSetObject.add(\"Love\");\r\n\r\nhashSetObject.add(\"Java\");\r\n\r\nif(hashSetObject.contains(\"I\")){\r\n\r\nSystem.out<\/em>.println(\"Hash Set Contains 'I'\");\r\n\r\n}\r\n\r\nelse{\r\n\r\nSystem.out<\/em>.println(\"Hash Set Do not Contains 'I'\");\r\n\r\n}\r\n\r\nif(hashSetObject.contains(\"India\")){\r\n\r\nSystem.out<\/em>.println(\"Hash Set Contains 'India'\");\r\n\r\n}\r\n\r\nelse{\r\n\r\nSystem.out<\/em>.println(\"Hash Set Do not Contains 'India'\");\r\n}\r\n}\r\n}\r\n<\/pre>\n
Output:<\/strong><\/span><\/p>\n
Hash Set Contains 'I'\r\n\r\nHash Set Do not Contains 'India'<\/pre>\n
Read All HashSet Methods With Example in Java<\/a><\/p>\n
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\u00a0Example of <\/strong>HashSet <\/strong>class<\/strong><\/h4>\n
Let us discuss Hash set with the help of program; following program has been divided into 3 Steps that we will discuss one by one.<\/p>\n
import java.util.*;\r\n\r\npublic class HashSetDemo{\r\n\r\npublic static void main(String args[]){\r\n\/\/Step: 1\r\nHashSet <String> hashSetObject= new HashSet <String>();\r\n\r\n\/\/Step: 2\r\n\r\nhashSetObject.add(\"I\"); \r\n\r\nhashSetObject.add(\"Love\");\r\n\r\nhashSetObject.add(\"Java\");\r\n\r\nhashSetObject.add(\"Java\");\r\n\r\nhashSetObject.add(\"I\");\r\n\r\n\/\/Step: 3\r\n\r\nSystem.out<\/em>.println(\"Values in HashSet are:\" +hashSetObject); ) \r\n}\r\n}\u00a0\r\n<\/pre>\n