【 Java 设计模式 】 单例模式

推荐单例模式

/**
 * 单例模式 - 饿汉式
 */
class Singleton {
    private Singleton() {
    }

    private static final Singleton instance = new Singleton();

    public static Singleton getInstance() {
        return instance;
    }
}

/**
 * 单例模式 - 双检锁
 */
class Singleton1 {
    private Singleton1() {
    }

    private static volatile Singleton1 instance = null;

    public static Singleton1 getInstance() {
        if (null == instance) {
            synchronized (Singleton1.class) {
                if (null == instance) {
                    instance = new Singleton1();
                }
            }
        }
        return instance;
    }
}

/**
 * 单例模式 - 静态内部类
 */
class Singleton2 {
    private Singleton2() {
    }

    public static Singleton2 getInstance() {
        return SingletonInstance.instance;
    }

    private static class SingletonInstance {
        private static final Singleton2 instance = new Singleton2();
    }
}

/**
 * 单例模式 - 枚举
 */
enum Singleton3 {
    Instance;

    public void say(String s) {
        System.out.println(s);
    }
}