使用枚举构造Singleton对象

本是古典何须时尚 2022-06-04 05:37 150阅读 0赞

### 单例的常见写法： ###

#### **私有构造器与静态成员** ####

public class SimpleSingletonY {
    
        public static final SimpleSingletonY INSTANCE = new SimpleSingletonY();
    
        private SimpleSingletonY() {
        }
    }

#### **静态工厂** ####

public class SimpleSingletonX {
        private static final SimpleSingletonX INSTANCE = new SimpleSingletonX();
    
        private SimpleSingletonX() {
        }
    
        public static SimpleSingletonX getInstance() {
            return INSTANCE;
        }
    }

#### **Double Check与懒加载** ####

public class DoubleCheckSingleton {
    
        private static volatile DoubleCheckSingleton INSTANCE = null;
        private DoubleCheckSingleton() {}
        public static DoubleCheckSingleton getInstance() {
            if (INSTANCE == null) {
                synchronized (DoubleCheckSingleton.class) {
                    if (INSTANCE == null) {
                        INSTANCE = new DoubleCheckSingleton();
                    }
                }
            }
            return INSTANCE;
        }
    
    }

> 懒加载可以避免JVM在加载Singleton这个类时对INSTANCE初始化操作（如果new的过程很耗时的话，应用程序启动的会很慢，降低体验的友好性，只在使用的时候进行初始化操作。

#### **另一种安全高效的懒加载实现方式** ####

public class StaticLazyLoadSingleton {
        private StaticLazyLoadSingleton() {}
    
        private static class LazyHolder {
            static final StaticLazyLoadSingleton INSTANCE = new StaticLazyLoadSingleton();
        }
    
        public static StaticLazyLoadSingleton getInstance() {
            return LazyHolder.INSTANCE;
        }
    }

#### **使用枚举** ####

public enum EnumSingleton {
        INSTANCE;
    
        int value;
    
        public int getValue() {
            return value;
        }
    
        public void setValue(int value) {
            this.value = value;
        }
    }

[https://en.wikipedia.org/wiki/Initialization-on-demand\_holder\_idiom][https_en.wikipedia.org_wiki_Initialization-on-demand_holder_idiom]

[https://dzone.com/articles/java-singletons-using-enum?fromrel=true][https_dzone.com_articles_java-singletons-using-enum_fromrel_true]

[https_en.wikipedia.org_wiki_Initialization-on-demand_holder_idiom]: https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom
[https_dzone.com_articles_java-singletons-using-enum_fromrel_true]: https://dzone.com/articles/java-singletons-using-enum?fromrel=true