java实现单列模式的七种方式

来源：互联网发布：理财小知识知乎编辑：程序博客网时间：2024/06/05 09:53
public class Test02 {      /**      * 单例模式，懒汉式，线程安全      */      public static class Singleton {          private final static Singleton INSTANCE = new Singleton();          private Singleton() {          }          public static Singleton getInstance() {              return INSTANCE;          }      }        /**      * 单例模式，饿汉式，线程不安全      */      public static class Singleton2 {          private static Singleton2 instance = null;          private Singleton2() {          }          public static Singleton2 getInstance() {              if (instance == null) {                  instance = new Singleton2();              }              return instance;          }      }      /**      * 单例模式，饿汉式，线程安全，多线程环境下效率不高      */      public static class Singleton3 {          private static Singleton3 instance = null;          private Singleton3() {          }          public static synchronized Singleton3 getInstance() {              if (instance == null) {                  instance = new Singleton3();              }              return instance;          }      }      /**      * 单例模式，懒汉式，变种，线程安全      */      public static class Singleton4 {          private static Singleton4 instance = null;          static {              instance = new Singleton4();          }          private Singleton4() {          }          public static Singleton4 getInstance() {              return instance;          }      }      /**      * 单例模式，使用静态内部类，线程安全【推荐】      */      public static class Singleton5 {          private final static class SingletonHolder {              private static final Singleton5 INSTANCE = new Singleton5();          }          private Singleton5() {          }          public static Singleton5 getInstance() {              return SingletonHolder.INSTANCE;          }      }      /**      * 静态内部类，使用枚举方式，线程安全【推荐】      */      public enum Singleton6 {          INSTANCE;          public void whateverMethod() {          }      }      /**      * 静态内部类，使用双重校验锁，线程安全【推荐】      */      public static class Singleton7 {          private volatile static Singleton7 instance = null;          private Singleton7() {          }          public static Singleton7 getInstance() {              if (instance == null) {                  synchronized (Singleton7.class) {                      if (instance == null) {                          instance = new Singleton7();                      }                  }              }              return instance;          }      }      public static void main(String[] args) {          System.out.println(Singleton.getInstance() == Singleton.getInstance());          System.out.println(Singleton2.getInstance() == Singleton2.getInstance());          System.out.println(Singleton3.getInstance() == Singleton3.getInstance());          System.out.println(Singleton4.getInstance() == Singleton4.getInstance());          System.out.println(Singleton5.getInstance() == Singleton5.getInstance());          System.out.println(Singleton6.INSTANCE == Singleton6.INSTANCE);          System.out.println(Singleton7.getInstance() == Singleton7.getInstance());      }  }
运行结果：
0 0