{"id":18359,"date":"2024-03-15T16:45:56","date_gmt":"2024-03-15T16:45:56","guid":{"rendered":"https:\/\/www.silicloud.com\/blog\/how-to-implement-the-state-design-pattern-in-java\/"},"modified":"2024-03-21T13:07:11","modified_gmt":"2024-03-21T13:07:11","slug":"how-to-implement-the-state-design-pattern-in-java","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/blog\/how-to-implement-the-state-design-pattern-in-java\/","title":{"rendered":"How to implement the State design pattern in Java?"},"content":{"rendered":"<p>The state pattern is a type of behavioral design pattern that allows an object to change its behavior when its internal state changes. In the state pattern, an object&#8217;s behavior is determined by its state.<\/p>\n<p>Below is a simple implementation of the State Pattern.<\/p>\n<ol>\n<li>Define a state interface (State) that declares the behavior methods of an object.<\/li>\n<li>Each concrete state class that implements the state interface has its own implementation of the methods defined in the state interface.<\/li>\n<li>Hold a state object in the context that can switch between different states.<\/li>\n<li>Provide a method in the context class (e.g. setState) to toggle the state.<\/li>\n<li>In the context class, call the corresponding action method based on the current state.<\/li>\n<\/ol>\n<p>Here is a simple Java code implementation:<\/p>\n<pre class=\"post-pre\"><code><span class=\"hljs-comment\">\/\/ \u5b9a\u4e49\u72b6\u6001\u63a5\u53e3<\/span>\r\n<span class=\"hljs-keyword\">interface<\/span> <span class=\"hljs-title class_\">State<\/span> {\r\n    <span class=\"hljs-keyword\">void<\/span> <span class=\"hljs-title function_\">doAction<\/span><span class=\"hljs-params\">(Context context)<\/span>;\r\n}\r\n\r\n<span class=\"hljs-comment\">\/\/ \u5b9e\u73b0\u5177\u4f53\u72b6\u6001\u7c7b<\/span>\r\n<span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title class_\">StartState<\/span> <span class=\"hljs-keyword\">implements<\/span> <span class=\"hljs-title class_\">State<\/span> {\r\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">void<\/span> <span class=\"hljs-title function_\">doAction<\/span><span class=\"hljs-params\">(Context context)<\/span> {\r\n        System.out.println(<span class=\"hljs-string\">\"Player is in start state\"<\/span>);\r\n        context.setState(<span class=\"hljs-built_in\">this<\/span>);\r\n    }\r\n}\r\n\r\n<span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title class_\">StopState<\/span> <span class=\"hljs-keyword\">implements<\/span> <span class=\"hljs-title class_\">State<\/span> {\r\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">void<\/span> <span class=\"hljs-title function_\">doAction<\/span><span class=\"hljs-params\">(Context context)<\/span> {\r\n        System.out.println(<span class=\"hljs-string\">\"Player is in stop state\"<\/span>);\r\n        context.setState(<span class=\"hljs-built_in\">this<\/span>);\r\n    }\r\n}\r\n\r\n<span class=\"hljs-comment\">\/\/ \u4e0a\u4e0b\u6587\u7c7b<\/span>\r\n<span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title class_\">Context<\/span> {\r\n    <span class=\"hljs-keyword\">private<\/span> State state;\r\n\r\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-title function_\">Context<\/span><span class=\"hljs-params\">()<\/span> {\r\n        state = <span class=\"hljs-literal\">null<\/span>;\r\n    }\r\n\r\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">void<\/span> <span class=\"hljs-title function_\">setState<\/span><span class=\"hljs-params\">(State state)<\/span> {\r\n        <span class=\"hljs-built_in\">this<\/span>.state = state;\r\n    }\r\n\r\n    <span class=\"hljs-keyword\">public<\/span> State <span class=\"hljs-title function_\">getState<\/span><span class=\"hljs-params\">()<\/span> {\r\n        <span class=\"hljs-keyword\">return<\/span> state;\r\n    }\r\n}\r\n\r\n<span class=\"hljs-comment\">\/\/ \u6d4b\u8bd5\u4ee3\u7801<\/span>\r\n<span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title class_\">StatePatternDemo<\/span> {\r\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">static<\/span> <span class=\"hljs-keyword\">void<\/span> <span class=\"hljs-title function_\">main<\/span><span class=\"hljs-params\">(String[] args)<\/span> {\r\n        <span class=\"hljs-type\">Context<\/span> <span class=\"hljs-variable\">context<\/span> <span class=\"hljs-operator\">=<\/span> <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-title class_\">Context<\/span>();\r\n\r\n        <span class=\"hljs-type\">StartState<\/span> <span class=\"hljs-variable\">startState<\/span> <span class=\"hljs-operator\">=<\/span> <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-title class_\">StartState<\/span>();\r\n        startState.doAction(context);\r\n\r\n        <span class=\"hljs-type\">StopState<\/span> <span class=\"hljs-variable\">stopState<\/span> <span class=\"hljs-operator\">=<\/span> <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-title class_\">StopState<\/span>();\r\n        stopState.doAction(context);\r\n    }\r\n}\r\n<\/code><\/pre>\n<p>When running the above code, the output will be:<\/p>\n<pre class=\"post-pre\"><code>Player is in start state\r\nPlayer is in stop state\r\n<\/code><\/pre>\n<p>In the example above, the State interface defines a behavior method doAction, and the StartState and StopState are concrete state classes that each implement the doAction method. The Context class holds a state object that can switch between different states. In the test code, we first create a Context object, then create a StartState object and use the doAction method to switch the Context object&#8217;s state to StartState; then create a StopState object and use the doAction method to switch the Context object&#8217;s state to StopState.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The state pattern is a type of behavioral design pattern that allows an object to change its behavior when its internal state changes. In the state pattern, an object&#8217;s behavior is determined by its state. Below is a simple implementation of the State Pattern. Define a state interface (State) that declares the behavior methods of [&hellip;]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_import_markdown_pro_load_document_selector":0,"_import_markdown_pro_submit_text_textarea":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-18359","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"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>How to implement the State design pattern in Java? - Blog - Silicon Cloud<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.silicloud.com\/blog\/how-to-implement-the-state-design-pattern-in-java\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"How to implement the State design pattern in Java?\" \/>\n<meta property=\"og:description\" content=\"The state pattern is a type of behavioral design pattern that allows an object to change its behavior when its internal state changes. 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