{"id":288,"date":"2025-06-29T14:13:15","date_gmt":"2025-06-29T14:13:15","guid":{"rendered":"https:\/\/thetestdata.com\/blog\/?p=288"},"modified":"2025-07-16T10:18:52","modified_gmt":"2025-07-16T10:18:52","slug":"difference-between-hash-map-and-hash-set","status":"publish","type":"post","link":"https:\/\/thetestdata.com\/blog\/difference-between-hash-map-and-hash-set\/","title":{"rendered":"Difference between Hash Map and Hash Set?"},"content":{"rendered":"\n<p>\ud83d\udd39<strong> What is a HashMap?<\/strong><\/p>\n\n\n\n<p>A <strong>HashMap<\/strong> in Java is a data structure that stores data in <strong>key-value pairs<\/strong>. It belongs to the <code>java.util<\/code> package and implements the <code>Map<\/code> interface.<\/p>\n\n\n\n<p>\u2705 Key Characteristics:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Stores data as (key, value)<\/strong> pairs.<\/li>\n\n\n\n<li><strong>Keys must be unique<\/strong>, but values can be duplicated.<\/li>\n\n\n\n<li>Allows <strong>one null key<\/strong> and <strong>multiple null values<\/strong>.<\/li>\n\n\n\n<li><strong>Not synchronized<\/strong> (not thread-safe by default).<\/li>\n\n\n\n<li>Offers <strong>constant-time performance<\/strong> for basic operations like <code>put()<\/code> and <code>get()<\/code>.<\/li>\n<\/ul>\n\n\n\n<p>\ud83e\udde0 Internal Working:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Internally uses a <strong>hash table<\/strong>.<\/li>\n\n\n\n<li>When you insert a key, its <code>hashCode()<\/code> is computed to determine the bucket location.<\/li>\n\n\n\n<li>If two keys have the same hash, a <strong>collision<\/strong> occurs, and the map handles it using a <strong>linked list<\/strong> or <strong>tree<\/strong> (in newer Java versions).<\/li>\n<\/ul>\n\n\n\n<p>\ud83e\uddea Example:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"997\" height=\"180\" src=\"https:\/\/thetestdata.com\/blog\/wp-content\/uploads\/2025\/06\/image-18.png\" alt=\"\" class=\"wp-image-289\" srcset=\"https:\/\/thetestdata.com\/blog\/wp-content\/uploads\/2025\/06\/image-18.png 997w, https:\/\/thetestdata.com\/blog\/wp-content\/uploads\/2025\/06\/image-18-300x54.png 300w, https:\/\/thetestdata.com\/blog\/wp-content\/uploads\/2025\/06\/image-18-768x139.png 768w\" sizes=\"auto, (max-width: 997px) 100vw, 997px\" \/><\/figure>\n\n\n\n<p>\ud83d\udd39 <strong>What is a HashSet?<\/strong><\/p>\n\n\n\n<p>A <strong>HashSet<\/strong> is a collection that stores <strong>unique elements only<\/strong>. It implements the <code>Set<\/code> interface and is also part of the <code>java.util<\/code> package.<\/p>\n\n\n\n<p>\u2705 Key Characteristics:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>No duplicate elements<\/strong> allowed.<\/li>\n\n\n\n<li><strong>No key-value mapping<\/strong>\u2014just values.<\/li>\n\n\n\n<li>Allows <strong>one null element<\/strong>.<\/li>\n\n\n\n<li><strong>Unordered<\/strong>\u2014does not maintain insertion order.<\/li>\n\n\n\n<li>Internally backed by a <strong>HashMap<\/strong>.<\/li>\n<\/ul>\n\n\n\n<p>\ud83e\udde0 Internal Working:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Each element in the <code>HashSet<\/code> is stored as a <strong>key<\/strong> in an internal <code>HashMap<\/code>, with a constant dummy value.<\/li>\n\n\n\n<li>This is why it ensures <strong>uniqueness<\/strong>\u2014because keys in a map must be unique.<\/li>\n<\/ul>\n\n\n\n<p>\ud83e\uddea Example:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"982\" height=\"178\" src=\"https:\/\/thetestdata.com\/blog\/wp-content\/uploads\/2025\/06\/image-19.png\" alt=\"\" class=\"wp-image-290\" srcset=\"https:\/\/thetestdata.com\/blog\/wp-content\/uploads\/2025\/06\/image-19.png 982w, https:\/\/thetestdata.com\/blog\/wp-content\/uploads\/2025\/06\/image-19-300x54.png 300w, https:\/\/thetestdata.com\/blog\/wp-content\/uploads\/2025\/06\/image-19-768x139.png 768w\" sizes=\"auto, (max-width: 982px) 100vw, 982px\" \/><\/figure>\n\n\n\n<p>\ud83e\udde0 Summary:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Feature<\/th><th>HashMap<\/th><th>HashSet<\/th><\/tr><\/thead><tbody><tr><td>Interface<\/td><td>Implements <code>Map<\/code><\/td><td>Implements <code>Set<\/code><\/td><\/tr><tr><td>Stores<\/td><td>Key-value pairs<\/td><td>Unique values only<\/td><\/tr><tr><td>Allows Duplicates<\/td><td>Keys: No, Values: Yes<\/td><td>No duplicates at all<\/td><\/tr><tr><td>Null Handling<\/td><td>One null key, many null values<\/td><td>One null element<\/td><\/tr><tr><td>Internal Use<\/td><td>Hash table<\/td><td>Backed by a HashMap<\/td><\/tr><\/tbody><\/table><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>Learn the key differences between HashMap and HashSet in Java. Understand their roles in key-value mapping vs unique element storage in data handling.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"site-container-style":"default","site-container-layout":"default","site-sidebar-layout":"default","disable-article-header":"default","disable-site-header":"default","disable-site-footer":"default","disable-content-area-spacing":"default","footnotes":""},"categories":[17],"tags":[],"class_list":["post-288","post","type-post","status-publish","format-standard","hentry","category-java-interview-questions"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/thetestdata.com\/blog\/wp-json\/wp\/v2\/posts\/288","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/thetestdata.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/thetestdata.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/thetestdata.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/thetestdata.com\/blog\/wp-json\/wp\/v2\/comments?post=288"}],"version-history":[{"count":2,"href":"https:\/\/thetestdata.com\/blog\/wp-json\/wp\/v2\/posts\/288\/revisions"}],"predecessor-version":[{"id":437,"href":"https:\/\/thetestdata.com\/blog\/wp-json\/wp\/v2\/posts\/288\/revisions\/437"}],"wp:attachment":[{"href":"https:\/\/thetestdata.com\/blog\/wp-json\/wp\/v2\/media?parent=288"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/thetestdata.com\/blog\/wp-json\/wp\/v2\/categories?post=288"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/thetestdata.com\/blog\/wp-json\/wp\/v2\/tags?post=288"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}