{"id":55,"date":"2018-05-06T08:00:00","date_gmt":"2018-05-06T00:00:00","guid":{"rendered":"https:\/\/liqimore.com\/2018\/enum-and-Singleton-Pattern\/"},"modified":"2022-03-21T02:28:56","modified_gmt":"2022-03-20T18:28:56","slug":"enum-and-singleton-pattern","status":"publish","type":"post","link":"https:\/\/liqimore.com\/2018\/enum-and-singleton-pattern\/","title":{"rendered":"\u679a\u4e3e\u548cJAVA\u7684\u5355\u4f8b\u6a21\u5f0f"},"content":{"rendered":"\n

\u679a\u4e3e<\/h2>\n\n\n\n

\u5b9a\u4e49\u679a\u4e3e\u7c7b<\/strong><\/p>\n\n\n\n

package com;\n\npublic enum Color {\n\n     RED, GREEN, BLANK, YELLOW\n\n}<\/pre>\n\n\n\n
\u7b80\u5355\u4f7f\u7528<\/strong><\/p>\n\n\n\n
package com;\n\npublic class B {\n\n    public static void main(String[] args) {\n\n\n        System.out.println( isRed( Color.BLANK ) ) ;  \/\/\u7ed3\u679c\uff1a false\n        System.out.println( isRed( Color.RED ) ) ;    \/\/\u7ed3\u679c\uff1a true\n\n    }\n\n\n    static boolean isRed( Color color ){\n        if ( Color.RED.equals( color )) {\n            return true ;\n        }\n        return false ;\n    }\n\n}<\/pre>\n\n\n\n
\u81ea\u5b9a\u4e49\u51fd\u6570<\/strong><\/p>\n\n\n\n
package com;\n\npublic enum Color {\n\n     RED(\"\u7ea2\u8272\", 1), GREEN(\"\u7eff\u8272\", 2), BLANK(\"\u767d\u8272\", 3), YELLO(\"\u9ec4\u8272\", 4);\n\n\n    private String name ;\n    private int index ;\n\n    private Color( String name , int index ){\n        this.name = name ;\n        this.index = index ;\n    }\n\n    public String getName() {\n        return name;\n    }\n    public void setName(String name) {\n        this.name = name;\n    }\n    public int getIndex() {\n        return index;\n    }\n    public void setIndex(int index) {\n        this.index = index;\n    }\n\n\n}<\/pre>\n\n\n\n
\u4f7f\u7528:<\/p>\n\n\n\n
package com;\n\npublic class B {\n\n    public static void main(String[] args) {\n\n        \/\/\u8f93\u51fa\u67d0\u4e00\u679a\u4e3e\u7684\u503c\n        System.out.println( Color.RED.getName() );\n        System.out.println( Color.RED.getIndex() );\n\n        \/\/\u904d\u5386\u6240\u6709\u7684\u679a\u4e3e\n        for( Color color : Color.values()){\n            System.out.println( color + \"  name: \" + color.getName() + \"  index: \" + color.getIndex() );\n        }\n    }\n\n}<\/pre>\n\n\n\n
\u8f93\u51fa\u7ed3\u679c:<\/strong><\/p>\n\n\n\n
\u7ea2\u8272  \n1  \nRED name: \u7ea2\u8272 index: 1  \nGREEN name: \u7eff\u8272 index: 2  \nBLANK name: \u767d\u8272 index: 3  \nYELLO name: \u9ec4\u8272 index: 4  <\/pre>\n\n\n\n
\u9664\u4e86\u679a\u4e3e,\u4ea6\u53ef\u4ee5\u4f7f\u7528 public static final<\/strong> \u6765\u5b9e\u73b0\u7c7b\u4f3c\u679a\u4e3e\u7684\u6548\u679c.<\/p>\n\n\n\n
\n\n\n\n
# \u5355\u4f8b\u6a21\u5f0f\u5355\u4f8b\u6a21\u5f0f\uff08Singleton Pattern\uff09\u662f Java \u4e2d\u6700\u7b80\u5355\u7684\u8bbe\u8ba1\u6a21\u5f0f\u4e4b\u4e00\u3002\u8fd9\u79cd\u7c7b\u578b\u7684\u8bbe\u8ba1\u6a21\u5f0f\u5c5e\u4e8e\u521b\u5efa\u578b\u6a21\u5f0f\uff0c\u5b83\u63d0\u4f9b\u4e86\u4e00\u79cd\u521b\u5efa\u5bf9\u8c61\u7684\u6700\u4f73\u65b9\u5f0f\u3002<\/p>\n\n\n\n
\u8fd9\u79cd\u6a21\u5f0f\u6d89\u53ca\u5230\u4e00\u4e2a\u5355\u4e00\u7684\u7c7b\uff0c\u8be5\u7c7b\u8d1f\u8d23\u521b\u5efa\u81ea\u5df1\u7684\u5bf9\u8c61\uff0c\u540c\u65f6\u786e\u4fdd\u53ea\u6709\u5355\u4e2a\u5bf9\u8c61\u88ab\u521b\u5efa\u3002\u8fd9\u4e2a\u7c7b\u63d0\u4f9b\u4e86\u4e00\u79cd\u8bbf\u95ee\u5176\u552f\u4e00\u7684\u5bf9\u8c61\u7684\u65b9\u5f0f\uff0c\u53ef\u4ee5\u76f4\u63a5\u8bbf\u95ee\uff0c\u4e0d\u9700\u8981\u5b9e\u4f8b\u5316\u8be5\u7c7b\u7684\u5bf9\u8c61\u3002<\/p>\n\n\n\n
\u6ce8\u610f\uff1a<\/strong><\/p>\n\n\n\n
1\u3001\u5355\u4f8b\u7c7b\u53ea\u80fd\u6709\u4e00\u4e2a\u5b9e\u4f8b\u3002
2\u3001\u5355\u4f8b\u7c7b\u5fc5\u987b\u81ea\u5df1\u521b\u5efa\u81ea\u5df1\u7684\u552f\u4e00\u5b9e\u4f8b\u3002
3\u3001\u5355\u4f8b\u7c7b\u5fc5\u987b\u7ed9\u6240\u6709\u5176\u4ed6\u5bf9\u8c61\u63d0\u4f9b\u8fd9\u4e00\u5b9e\u4f8b\u3002<\/p>\n\n\n\n
\u5b9e\u73b0\u65b9\u6cd5:<\/strong>
\u901a\u5e38\u60c5\u51b5\u4e0b\uff0c\u6211\u4eec\u5199\u5355\u4f8b\u6a21\u5f0f\u7684\u65f6\u5019\u65e0\u975e\u5c31\u662f\u4e09\u4e2a\u6b65\u9aa4\uff1a\u6784\u9020\u5668\u79c1\u6709\u5316\uff0c\u58f0\u660e\u79c1\u6709\u9759\u6001\u53d8\u91cf\uff0c\u63d0\u4f9b\u9759\u6001\u83b7\u53d6\u5b9e\u4f8b\u7684\u65b9\u6cd5\u3002\u7b80\u5355\u8bf4\u5c31\u662f\u4ee5\u4e0b\u8fd9\u79cd\u65b9\u5f0f(\u997f\u6c49)\uff1a<\/p>\n\n\n\n
class SingletonA {\n    \/\/\u79c1\u6709\u9759\u6001\u5b9e\u4f8b\u53d8\u91cf\n    private static SingletonA instence = new SingletonA();\n    \/\/\u79c1\u6709\u6784\u9020\u5668\n    private SingletonA() {\n    }\n    \/\/\u516c\u6709\u83b7\u53d6\u9759\u6001\u5b9e\u4f8b\u7684\u65b9\u6cd5\n    public static SingletonA getInstance() {\n        return instence;\n    }\n}<\/pre>\n\n\n\n
\u8fd9\u662f\u6700\u57fa\u672c\u7684\u5355\u4f8b\u6a21\u5f0f\u7684\u5199\u6cd5\uff0c\u8003\u8651\u5230\u7ebf\u7a0b\u5b89\u5168\u7684\u95ee\u9898\uff0c\u4f1a\u7528synchronized \u5173\u952e\u5b57\u4fee\u9970getInstance()\u65b9\u6cd5\uff0c\u53e6\u5916\u8fd8\u6709\u997f\u6c49\u5f0f\u3001\u61d2\u6c49\u5f0f\u3001\u9759\u6001\u5185\u90e8\u7c7b\u3001\u53cc\u91cd\u6821\u9a8c\u9501\u7684\u5199\u6cd5\u3002
\u4f46\u662f\u8fd9\u79cd\u5199\u6cd5\u5b58\u5728\u7f3a\u9677\uff0c\u53ef\u4ee5\u5229\u7528\u53cd\u5c04\u7684\u65b9\u5f0f\u6765\u5b9e\u4f8b\u5316\u591a\u4e2a\u4e0d\u540c\u7684\u5b9e\u4f8b.
\u8be6\u7ec6\u505a\u6cd5\u53c2\u8003: \u6d45\u8c08\u4f7f\u7528\u5355\u5143\u7d20\u7684\u679a\u4e3e\u7c7b\u578b\u5b9e\u73b0\u5355\u4f8b\u6a21\u5f0f<\/a><\/p>\n\n\n\n
\u7b2c\u4e00\u79cd\uff08\u61d2\u6c49\uff0c\u7ebf\u7a0b\u4e0d\u5b89\u5168\uff09:<\/strong><\/p>\n\n\n\n
public class SingletonDemo1 {\n    private static SingletonDemo1 instance;\n    private SingletonDemo1(){}\n    public static SingletonDemo1 getInstance(){\n        if (instance == null) {\n            instance = new SingletonDemo1();\n        }\n        return instance;\n    }\n}<\/pre>\n\n\n\n
\u8fd9\u79cd\u5199\u6cd5lazy loading\u5f88\u660e\u663e\uff0c\u4f46\u662f\u81f4\u547d\u7684\u662f\u5728\u591a\u7ebf\u7a0b\u4e0d\u80fd\u6b63\u5e38\u5de5\u4f5c\u3002\u3000<\/p>\n\n\n\n
\u7b2c\u4e8c\u79cd\uff08\u61d2\u6c49\uff0c\u7ebf\u7a0b\u5b89\u5168\uff09\uff1a<\/strong><\/p>\n\n\n\n
public class SingletonDemo2 {\n    \/\/\u4e0d\u5728\u8fd9\u91cc\u5b9e\u4f8b\u5316\n    private static SingletonDemo2 instance;\n    private SingletonDemo2(){}\n    public static synchronized SingletonDemo2 getInstance(){\n        if (instance == null) {\n            instance = new SingletonDemo2();\n        }\n        return instance;\n    }\n}<\/pre>\n\n\n\n
\u4f7f\u7528synchronized\u4fee\u9970\u4e86getInstance\u65b9\u6cd5.
\u8fd9\u79cd\u5199\u6cd5\u5728getInstance()\u65b9\u6cd5\u4e2d\u52a0\u5165\u4e86synchronized\u9501\u3002\u80fd\u591f\u5728\u591a\u7ebf\u7a0b\u4e2d\u5f88\u597d\u7684\u5de5\u4f5c\uff0c\u800c\u4e14\u770b\u8d77\u6765\u5b83\u4e5f\u5177\u5907\u5f88\u597d\u7684lazy loading\uff0c\u4f46\u662f\u6548\u7387\u5f88\u4f4e\uff08\u56e0\u4e3a\u9501\uff09\uff0c\u5e76\u4e14\u5927\u591a\u6570\u60c5\u51b5\u4e0b\u4e0d\u9700\u8981\u540c\u6b65\u3002<\/p>\n\n\n\n
\u7b2c\u4e09\u79cd\uff08\u997f\u6c49\uff09\uff1a<\/strong><\/p>\n\n\n\n
public class SingletonDemo3 {\n    private static SingletonDemo3 instance = new SingletonDemo3();\n    private SingletonDemo3(){}\n    public static SingletonDemo3 getInstance(){\n        return instance;\n    }\n}<\/pre>\n\n\n\n
\u8fd9\u79cd\u65b9\u5f0f\u57fa\u4e8eclassloder\u673a\u5236\u907f\u514d\u4e86\u591a\u7ebf\u7a0b\u7684\u540c\u6b65\u95ee\u9898\uff0c\u4e0d\u8fc7\uff0cinstance\u5728\u7c7b\u88c5\u8f7d\u65f6\u5c31\u5b9e\u4f8b\u5316\uff0c\u8fd9\u65f6\u5019\u521d\u59cb\u5316instance\u663e\u7136\u6ca1\u6709\u8fbe\u5230lazy loading\u7684\u6548\u679c\u3002<\/p>\n\n\n\n
\u7b2c\u56db\u79cd\uff08\u997f\u6c49\uff0c\u53d8\u79cd\uff09\uff1a<\/strong><\/p>\n\n\n\n
public class SingletonDemo4 {\n    private static SingletonDemo4 instance = null;\n    static{\n        instance = new SingletonDemo4();\n    }\n    private SingletonDemo4(){}\n    public static SingletonDemo4 getInstance(){\n        return instance;\n    }\n}<\/pre>\n\n\n\n
\u8868\u9762\u4e0a\u770b\u8d77\u6765\u5dee\u522b\u633a\u5927\uff0c\u5176\u5b9e\u66f4\u7b2c\u4e09\u79cd\u65b9\u5f0f\u5dee\u4e0d\u591a\uff0c\u90fd\u662f\u5728\u7c7b\u521d\u59cb\u5316\u5373\u5b9e\u4f8b\u5316instance<\/p>\n\n\n\n
\u7b2c\u4e94\u79cd\uff08\u9759\u6001\u5185\u90e8\u7c7b\uff09\uff1a<\/strong><\/p>\n\n\n\n
public class SingletonDemo5 {\n    private static class SingletonHolder{\n        private static final SingletonDemo5 instance = new SingletonDemo5();\n    }\n    private SingletonDemo5(){}\n    public static final SingletonDemo5 getInsatance(){\n        return SingletonHolder.instance;\n    }\n}<\/pre>\n\n\n\n
\u8fd9\u79cd\u65b9\u5f0f\u540c\u6837\u5229\u7528\u4e86classloder\u7684\u673a\u5236\u6765\u4fdd\u8bc1\u521d\u59cb\u5316instance\u65f6\u53ea\u6709\u4e00\u4e2a\u7ebf\u7a0b\uff0c\u5b83\u8ddf\u7b2c\u4e09\u79cd\u548c\u7b2c\u56db\u79cd\u65b9\u5f0f\u4e0d\u540c\u7684\u662f\uff08\u5f88\u7ec6\u5fae\u7684\u5dee\u522b\uff09\uff1a\u7b2c\u4e09\u79cd\u548c\u7b2c\u56db\u79cd\u65b9\u5f0f\u662f\u53ea\u8981Singleton\u7c7b\u88ab\u88c5\u8f7d\u4e86\uff0c\u90a3\u4e48instance\u5c31\u4f1a\u88ab\u5b9e\u4f8b\u5316\uff08\u6ca1\u6709\u8fbe\u5230lazy loading\u6548\u679c\uff09\uff0c\u800c\u8fd9\u79cd\u65b9\u5f0f\u662fSingleton\u7c7b\u88ab\u88c5\u8f7d\u4e86\uff0cinstance\u4e0d\u4e00\u5b9a\u88ab\u521d\u59cb\u5316\u3002\u56e0\u4e3aSingletonHolder\u7c7b\u6ca1\u6709\u88ab\u4e3b\u52a8\u4f7f\u7528\uff0c\u53ea\u6709\u663e\u793a\u901a\u8fc7\u8c03\u7528getInstance\u65b9\u6cd5\u65f6\uff0c\u624d\u4f1a\u663e\u793a\u88c5\u8f7dSingletonHolder\u7c7b\uff0c\u4ece\u800c\u5b9e\u4f8b\u5316instance\u3002\u60f3\u8c61\u4e00\u4e0b\uff0c\u5982\u679c\u5b9e\u4f8b\u5316instance\u5f88\u6d88\u8017\u8d44\u6e90\uff0c\u6211\u60f3\u8ba9\u4ed6\u5ef6\u8fdf\u52a0\u8f7d\uff0c\u53e6\u5916\u4e00\u65b9\u9762\uff0c\u6211\u4e0d\u5e0c\u671b\u5728Singleton\u7c7b\u52a0\u8f7d\u65f6\u5c31\u5b9e\u4f8b\u5316\uff0c\u56e0\u4e3a\u6211\u4e0d\u80fd\u786e\u4fddSingleton\u7c7b\u8fd8\u53ef\u80fd\u5728\u5176\u4ed6\u7684\u5730\u65b9\u88ab\u4e3b\u52a8\u4f7f\u7528\u4ece\u800c\u88ab\u52a0\u8f7d\uff0c\u90a3\u4e48\u8fd9\u4e2a\u65f6\u5019\u5b9e\u4f8b\u5316instance\u663e\u7136\u662f\u4e0d\u5408\u9002\u7684\u3002\u8fd9\u4e2a\u65f6\u5019\uff0c\u8fd9\u79cd\u65b9\u5f0f\u76f8\u6bd4\u7b2c\u4e09\u548c\u7b2c\u56db\u79cd\u65b9\u6cd5\u5c31 \u663e\u5f97\u66f4\u5408\u7406<\/strong>\u3002<\/p>\n\n\n\n
\u7b2c\u516d\u79cd\uff08\u679a\u4e3e\uff09\uff1a<\/strong><\/p>\n\n\n\n
public enum SingletonDemo6 {\n    instance;\n    public void whateverMethod(){\n    }\n}<\/pre>\n\n\n\n
\u8fd9\u79cd\u65b9\u5f0f\u662fEffective Java\u4f5c\u8005Josh Bloch \u63d0\u5021\u7684\u65b9\u5f0f\uff0c\u5b83\u4e0d\u4ec5\u80fd\u907f\u514d\u591a\u7ebf\u7a0b\u540c\u6b65\u95ee\u9898\uff0c\u800c\u4e14\u8fd8\u80fd\u9632\u6b62\u53cd\u5e8f\u5217\u5316\u91cd\u65b0\u521b\u5efa\u65b0\u7684\u5bf9\u8c61\uff0c\u53ef\u8c13\u662f\u5f88\u575a\u5f3a\u7684\u58c1\u5792\u554a\uff0c\u4e0d\u8fc7\uff0c\u4e2a\u4eba\u8ba4\u4e3a\u7531\u4e8e1.5\u4e2d\u624d\u52a0\u5165enum\u7279\u6027\uff0c\u7528\u8fd9\u79cd\u65b9\u5f0f\u5199\u4e0d\u514d\u8ba9\u4eba\u611f\u89c9\u751f\u758f\uff0c\u5728\u5b9e\u9645\u5de5\u4f5c\u4e2d\uff0c\u6211\u4e5f\u5f88\u5c11\u770b\u89c1\u6709\u4eba\u8fd9\u4e48\u5199\u8fc7\u3002<\/p>\n\n\n\n
\u7b2c\u4e03\u79cd\uff08\u53cc\u91cd\u6821\u9a8c\u9501\uff09\uff1a<\/strong><\/p>\n\n\n\n
public class SingletonDemo7 {\n    private volatile static SingletonDemo7 singletonDemo7;\n    private SingletonDemo7(){}\n    public static SingletonDemo7 getSingletonDemo7(){\n        if (singletonDemo7 == null) {\n            synchronized (SingletonDemo7.class) {\n                if (singletonDemo7 == null) {\n                    singletonDemo7 = new SingletonDemo7();\n                }\n            }\n        }\n        return singletonDemo7;\n    }\n}<\/pre>\n\n\n\n
\u8fd9\u4e2a\u662f\u7b2c\u4e8c\u79cd\u65b9\u5f0f\u7684\u5347\u7ea7\u7248\uff0c\u4fd7\u79f0\u53cc\u91cd\u68c0\u67e5\u9501\u5b9a\uff0c\u8be6\u7ec6\u4ecb\u7ecd\u8bf7\u67e5\u770b\uff1ahttp:\/\/www.ibm.com\/developerworks\/cn\/java\/j-dcl.html<\/a>
\u5728JDK1.5\u4e4b\u540e\uff0c\u53cc\u91cd\u68c0\u67e5\u9501\u5b9a\u624d\u80fd\u591f\u6b63\u5e38\u8fbe\u5230\u5355\u4f8b\u6548\u679c\u3002<\/p>\n\n\n\n
\u53c2\u8003<\/h2>\n\n\n\n
\u6d45\u8c08\u4f7f\u7528\u5355\u5143\u7d20\u7684\u679a\u4e3e\u7c7b\u578b\u5b9e\u73b0\u5355\u4f8b\u6a21\u5f0f<\/a>
Java\u5b66\u4e60\u6574\u7406\u7cfb\u5217\u4e4bJava\u679a\u4e3e\u7c7b\u578b\u7684\u4f7f\u7528<\/a>
Java \u679a\u4e3e(enum) \u8be6\u89e37\u79cd\u5e38\u89c1\u7684\u7528\u6cd5<\/a>
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JAVA\u8bbe\u8ba1\u6a21\u5f0f\u4e4b\u5355\u4f8b\u6a21\u5f0f<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
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