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  • 单例模式的八种写法

    1、饿汉式(静态常量)[可用]

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

    2、饿汉式(静态代码块)[可用]

    public class Singleton {
    
        private static Singleton instance;
    
        static {
            instance = new Singleton();
        }
    
        private Singleton() {}
    
        public static Singleton getInstance() {
            return instance;
        }
    }
    public class Singleton {
    
        private static Singleton instance;
    
        static {
            instance = new Singleton();
        }
    
        private Singleton() {}
    
        public static Singleton getInstance() {
            return instance;
        }
    }

    3、懒汉式(线程不安全)[不可用]

    public class Singleton {
    
        private static Singleton singleton;
    
        private Singleton() {}
    
        public static Singleton getInstance() {
            if (singleton == null) {
                singleton = new Singleton();
            }
            return singleton;
        }
    }

    4、懒汉式(线程安全,同步方法)[不推荐用]

    public class Singleton {
    
        private static Singleton singleton;
    
        private Singleton() {}
    
        public static synchronized Singleton getInstance() {
            if (singleton == null) {
                singleton = new Singleton();
            }
            return singleton;
        }
    }

    5、懒汉式(线程安全,同步代码块)[不可用]

    public class Singleton {
    
        private static Singleton singleton;
    
        private Singleton() {}
    
        public static Singleton getInstance() {
            if (singleton == null) {
                synchronized (Singleton.class) {
                    singleton = new Singleton();
                }
            }
            return singleton;
        }
    }

    6、双重检查[推荐用]

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

    7、静态内部类[推荐用]

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

    8、枚举[推荐用]

    public enum Singleton {
        INSTANCE;
        public void whateverMethod() {
    
        }
    }
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  • 原文地址:https://www.cnblogs.com/2018cjx/p/12612718.html
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