HashSet<\/code> class of the Java Collections framework provides the functionalities of the hash table data structure.<\/p>\n\n\n\nIt implements the\u00a0Set interface.<\/p>\n\n\n\n![\"Java](\"https:\/\/cdn.programiz.com\/sites\/tutorial2program\/files\/java-hashset.png\")
<\/figure>\n\n\n\n
\n\n\n\nCreating a HashSet<\/h2>\n\n\n\n
In order to create a hash set, we must import the java.util.HashSet<\/code> package first.<\/p>\n\n\n\nOnce we import the package, here is how we can create hash sets in Java.<\/p>\n\n\n\n
\/\/ HashSet with 8 capacity and 0.75 load factor\nHashSet<Integer> numbers = new HashSet<>(8, 0.75);\n<\/code><\/pre>\n\n\n\nHere, we have created a hash set named numbers<\/code>.<\/p>\n\n\n\nNotice, the part new HashSet<>(8, 0.75)<\/code>. Here, the first parameter is capacity<\/strong>, and the second parameter is loadFactor<\/strong>.<\/p>\n\n\n\n- capacity<\/strong> – The capacity of this hash set is 8. Meaning, it can store 8 elements.<\/li>
- loadFactor<\/strong> – The load factor of this hash set is 0.6. This means, whenever our hash set is filled by 60%, the elements are moved to a new hash table of double the size of the original hash table.<\/li><\/ul>\n\n\n\n
Default capacity and load factor<\/strong><\/p>\n\n\n\nIt’s possible to create a hash table without defining its capacity and load factor. For example,<\/p>\n\n\n\n
\/\/ HashSet with default capacity and load factor\nHashSet<Integer> numbers1 = new HashSet<>();\n<\/code><\/pre>\n\n\n\nBy default,<\/p>\n\n\n\n
- the capacity of the hash set will be 16<\/li>
- the load factor will be 0.75<\/li><\/ul>\n\n\n\n
\n\n\n\nMethods of HashSet<\/h2>\n\n\n\n
The HashSet<\/code> class provides various methods that allow us to perform various operations on the set.<\/p>\n\n\n\n
\n\n\n\nInsert Elements to HashSet<\/h2>\n\n\n\nadd()<\/code> – inserts the specified element to the set<\/li>addAll()<\/code> – inserts all the elements of the specified collection to the set<\/li><\/ul>\n\n\n\nFor example,<\/p>\n\n\n\n
import java.util.HashSet;\n\nclass Main {\n public static void main(String[] args) {\n HashSet<Integer> evenNumber = new HashSet<>();\n\n \/\/ Using add() method\n evenNumber.add(2);\n evenNumber.add(4);\n evenNumber.add(6);\n System.out.println(\"HashSet: \" + evenNumber);\n\n HashSet<Integer> numbers = new HashSet<>();\n \n \/\/ Using addAll() method\n numbers.addAll(evenNumber);\n numbers.add(5);\n System.out.println(\"New HashSet: \" + numbers);\n }\n}\n<\/code><\/pre>\n\n\n\nOutput<\/strong><\/p>\n\n\n\nHashSet: [2, 4, 6]\nNew HashSet: [2, 4, 5, 6]\n<\/samp><\/code><\/pre>\n\n\n\n
\n\n\n\nAccess HashSet Elements<\/h2>\n\n\n\n
To access the elements of a hash set, we can use the iterator()<\/code> method. In order to use this method, we must import the java.util.Iterator<\/code> package. For example,<\/p>\n\n\n\nimport java.util.HashSet;\nimport java.util.Iterator;\n\nclass Main {\n public static void main(String[] args) {\n HashSet<Integer> numbers = new HashSet<>();\n numbers.add(2);\n numbers.add(5);\n numbers.add(6);\n System.out.println(\"HashSet: \" + numbers);\n\n \/\/ Calling iterator() method\n Iterator<Integer> iterate = numbers.iterator();\n System.out.print(\"HashSet using Iterator: \");\n \/\/ Accessing elements\n while(iterate.hasNext()) {\n System.out.print(iterate.next());\n System.out.print(\", \");\n }\n }\n}\n<\/code><\/pre>\n\n\n\nOutput<\/strong><\/p>\n\n\n\nHashSet: [2, 5, 6]\nHashSet using Iterator: 2, 5, 6,\n<\/samp><\/code><\/pre>\n\n\n\n
\n\n\n\nRemove Elements<\/h2>\n\n\n\nremove()<\/code> – removes the specified element from the set<\/li>removeAll()<\/code> – removes all the elements from the set<\/li><\/ul>\n\n\n\nFor example,<\/p>\n\n\n\n
import java.util.HashSet;\n\nclass Main {\n public static void main(String[] args) {\n HashSet<Integer> numbers = new HashSet<>();\n numbers.add(2);\n numbers.add(5);\n numbers.add(6);\n System.out.println(\"HashSet: \" + numbers);\n\n \/\/ Using remove() method\n boolean value1 = numbers.remove(5);\n System.out.println(\"Is 5 removed? \" + value1);\n\n boolean value2 = numbers.removeAll(numbers);\n System.out.println(\"Are all elements removed? \" + value2);\n }\n}\n<\/code><\/pre>\n\n\n\nOutput<\/strong><\/p>\n\n\n\nHashSet: [2, 5, 6]\nIs 5 removed? true\nAre all elements removed? true\n<\/samp><\/code><\/pre>\n\n\n\n
\n\n\n\nSet Operations<\/h2>\n\n\n\n
The various methods of the HashSet<\/code> class can also be used to perform various set operations.<\/p>\n\n\n\n
\n\n\n\nUnion of Sets<\/h2>\n\n\n\n
To perform the union between two sets, we can use the addAll()<\/code> method. For example,<\/p>\n\n\n\nimport java.util.HashSet;\n\nclass Main {\n public static void main(String[] args) {\n HashSet<Integer> evenNumbers = new HashSet<>();\n evenNumbers.add(2);\n evenNumbers.add(4);\n System.out.println(\"HashSet1: \" + evenNumbers);\n\n HashSet<Integer> numbers = new HashSet<>();\n numbers.add(1);\n numbers.add(3);\n System.out.println(\"HashSet2: \" + numbers);\n\n \/\/ Union of two set\n numbers.addAll(evenNumbers);\n System.out.println(\"Union is: \" + numbers);\n }\n}\n\n<\/code><\/pre>\n\n\n\nOutput<\/strong><\/p>\n\n\n\nHashSet1: [2, 4]\nHashSet2: [1, 3]\nUnion is: [1, 2, 3, 4]\n<\/samp><\/code><\/pre>\n\n\n\n
\n\n\n\nIntersection of Sets<\/h2>\n\n\n\n
To perform the intersection between two sets, we can use the retainAll()<\/code> method. For example<\/p>\n\n\n\nimport java.util.HashSet;\n\nclass Main {\n public static void main(String[] args) {\n HashSet<Integer> primeNumbers = new HashSet<>();\n primeNumbers.add(2);\n primeNumbers.add(3);\n System.out.println(\"HashSet1: \" + primeNumbers);\n\n HashSet<Integer> evenNumbers = new HashSet<>();\n evenNumbers.add(2);\n evenNumbers.add(4);\n System.out.println(\"HashSet2: \" + evenNumbers);\n\n \/\/ Intersection of two sets\n evenNumbers.retainAll(primeNumbers);\n System.out.println(\"Intersection is: \" + evenNumbers);\n }\n}\n<\/code><\/pre>\n\n\n\nOutput<\/strong><\/p>\n\n\n\nHashSet1: [2, 3]\nHashSet2: [2, 4]\nIntersection is: [2]\n<\/samp><\/code><\/pre>\n\n\n\n
\n\n\n\nDifference of Sets<\/h2>\n\n\n\n
To calculate the difference between the two sets, we can use the removeAll()<\/code> method. For example,<\/p>\n\n\n\nimport java.util.HashSet;\n\nclass Main {\n public static void main(String[] args) {\n HashSet<Integer> primeNumbers = new HashSet<>();\n primeNumbers.add(2);\n primeNumbers.add(3);\n primeNumbers.add(5);\n System.out.println(\"HashSet1: \" + primeNumbers);\n\n HashSet<Integer> oddNumbers = new HashSet<>();\n oddNumbers.add(1);\n oddNumbers.add(3);\n oddNumbers.add(5);\n System.out.println(\"HashSet2: \" + oddNumbers);\n\n \/\/ Difference between HashSet1 and HashSet2\n primeNumbers.removeAll(oddNumbers);\n System.out.println(\"Difference : \" + primeNumbers);\n }\n}\n<\/code><\/pre>\n\n\n\nOutput<\/strong><\/p>\n\n\n\nHashSet1: [2, 3, 5]\nHashSet2: [1, 3, 5]\nDifference: [2]\n<\/samp><\/code><\/pre>\n\n\n\n
\n\n\n\nSubset<\/h2>\n\n\n\n
To check if a set is a subset of another set or not, we can use the containsAll()<\/code> method. For example,<\/p>\n\n\n\nimport java.util.HashSet;\n\nclass Main {\n public static void main(String[] args) {\n HashSet<Integer> numbers = new HashSet<>();\n numbers.add(1);\n numbers.add(2);\n numbers.add(3);\n numbers.add(4);\n System.out.println(\"HashSet1: \" + numbers);\n\n HashSet<Integer> primeNumbers = new HashSet<>();\n primeNumbers.add(2);\n primeNumbers.add(3);\n System.out.println(\"HashSet2: \" + primeNumbers);\n\n \/\/ Check if primeNumbers is a subset of numbers\n boolean result = numbers.containsAll(primeNumbers);\n System.out.println(\"Is HashSet2 is subset of HashSet1? \" + result);\n }\n}\n<\/code><\/pre>\n\n\n\nOutput<\/strong><\/p>\n\n\n\nHashSet1: [1, 2, 3, 4]\nHashSet2: [2, 3]\nIs HashSet2 is a subset of HashSet1? true\n<\/samp><\/code><\/pre>\n\n\n\n
\n\n\n\nOther Methods Of HashSet<\/h2>\n\n\n\nMethod<\/th> Description<\/th><\/tr> clone()<\/code><\/td>Creates a copy of the HashSet<\/code><\/td><\/tr>contains()<\/code><\/td>Searches the HashSet<\/code> for the specified element and returns a boolean result<\/td><\/tr>isEmpty()<\/code><\/td>Checks if the HashSet<\/code> is empty<\/td><\/tr>size()<\/code><\/td>Returns the size of the HashSet<\/code><\/td><\/tr>clear()<\/code><\/td>Removes all the elements from the HashSet<\/code><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<\/p>\n\n\n\n
\n\n\n\nWhy HashSet?<\/h2>\n\n\n\n
In Java, HashSet<\/code> is commonly used if we have to access elements randomly. It is because elements in a hash table are accessed using hash codes.<\/p>\n\n\n\nThe hashcode of an element is a unique identity that helps to identify the element in a hash table.<\/p>\n\n\n\n
HashSet<\/code> cannot contain duplicate elements. Hence, each hash set element has a unique hashcode.<\/p>\n\n\n\nNote:<\/strong> HashSet is not synchronized. That is if multiple threads access the hash set at the same time and one of the threads modifies the hash set. Then it must be externally synchronized.<\/p>\n","protected":false},"excerpt":{"rendered":"In this tutorial, we will learn about the Java HashSet class. We will learn about different hash set methods and operations with the help of examples. The HashSet class of the Java Collections framework provides the functionalities of the hash table data structure. It implements the\u00a0Set interface. Creating a HashSet In order to create a hash set, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[428],"tags":[],"_links":{"self":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/1278"}],"collection":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/comments?post=1278"}],"version-history":[{"count":0,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/1278\/revisions"}],"wp:attachment":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/media?parent=1278"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/categories?post=1278"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/tags?post=1278"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}