{"id":13487,"date":"2024-03-15T07:13:16","date_gmt":"2024-03-15T07:13:16","guid":{"rendered":"https:\/\/www.silicloud.com\/blog\/what-is-the-usage-of-identityhashmap-in-java\/"},"modified":"2025-08-05T19:08:13","modified_gmt":"2025-08-05T19:08:13","slug":"what-is-the-usage-of-identityhashmap-in-java","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/blog\/what-is-the-usage-of-identityhashmap-in-java\/","title":{"rendered":"Java IdentityHashMap Usage Guide"},"content":{"rendered":"<p>IdentityHashMap in Java is a unique implementation of HashMap that uses object references as keys, instead of using the equals() and hashCode() methods to determine if objects are equal.<\/p>\n<p>The primary purpose of using IdentityHashMap is when there is a need to compare if two object references are equal, such as when there is a need to retain objects with different references, or when using objects as keys.<\/p>\n<p>The usage of IdentityHashMap is similar to HashMap, where you can add key-value pairs to the mapping using the put() method, retrieve values by keys using the get() method, and check for the existence of specific keys using the containsKey() method.<\/p>\n<p>Here is a simple example:<\/p>\n<pre class=\"post-pre\"><code>IdentityHashMap&lt;String, Integer&gt; map = <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-title class_\">IdentityHashMap<\/span>&lt;&gt;();\r\n\r\n<span class=\"hljs-comment\">\/\/ \u6dfb\u52a0\u952e\u503c\u5bf9<\/span>\r\nmap.put(<span class=\"hljs-string\">\"one\"<\/span>, <span class=\"hljs-number\">1<\/span>);\r\nmap.put(<span class=\"hljs-string\">\"two\"<\/span>, <span class=\"hljs-number\">2<\/span>);\r\nmap.put(<span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-title class_\">String<\/span>(<span class=\"hljs-string\">\"one\"<\/span>), <span class=\"hljs-number\">3<\/span>); <span class=\"hljs-comment\">\/\/ \u4e0d\u540c\u7684\u5f15\u7528\uff0c\u4ecd\u7136\u53ef\u4ee5\u6dfb\u52a0\u6210\u529f<\/span>\r\n\r\n<span class=\"hljs-comment\">\/\/ \u83b7\u53d6\u503c<\/span>\r\nSystem.out.println(map.get(<span class=\"hljs-string\">\"one\"<\/span>)); <span class=\"hljs-comment\">\/\/ \u8f93\u51fa3\uff0c\u56e0\u4e3a\u4f7f\u7528\u4e86\u4e0d\u540c\u7684\u5f15\u7528<\/span>\r\n\r\n<span class=\"hljs-comment\">\/\/ \u68c0\u67e5\u952e\u662f\u5426\u5b58\u5728<\/span>\r\nSystem.out.println(map.containsKey(<span class=\"hljs-string\">\"one\"<\/span>)); <span class=\"hljs-comment\">\/\/ \u8f93\u51fatrue<\/span>\r\n\r\n<span class=\"hljs-comment\">\/\/ \u904d\u5386\u6620\u5c04<\/span>\r\n<span class=\"hljs-keyword\">for<\/span> (Map.Entry&lt;String, Integer&gt; entry : map.entrySet()) {\r\n    System.out.println(entry.getKey() + <span class=\"hljs-string\">\" : \"<\/span> + entry.getValue());\r\n}\r\n<\/code><\/pre>\n<p>The output results in:<\/p>\n<pre class=\"post-pre\"><code>3\r\ntrue\r\none : 3\r\ntwo : 2\r\n<\/code><\/pre>\n<p>It is important to note that IdentityHashMap uses object references for comparing keys, rather than using the equals() and hashCode() methods, so it may not be suitable in some cases. In general, using HashMap should suffice for most needs.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>IdentityHashMap in Java is a unique implementation of HashMap that uses object references as keys, instead of using the equals() and hashCode() methods to determine if objects are equal. The primary purpose of using IdentityHashMap is when there is a need to compare if two object references are equal, such as when there is a [&hellip;]<\/p>\n","protected":false},"author":10,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_import_markdown_pro_load_document_selector":0,"_import_markdown_pro_submit_text_textarea":"","footnotes":""},"categories":[1],"tags":[17992,17991,578,92,17993],"class_list":["post-13487","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-hashmap-vs-identityhashmap","tag-identityhashmap","tag-java-collections","tag-java-tutorial","tag-object-references"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v21.5 (Yoast SEO v21.5) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Java IdentityHashMap Usage Guide - Blog - Silicon Cloud<\/title>\n<meta name=\"description\" content=\"Learn how IdentityHashMap in Java uses object references as keys. 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