Java单例

/**
 * @Author: DengJia
 * @Date: 2023/3/22
 * @Description: 单例
 */

public class Singleton {
    public static void main(String[] args) {
        System.out.println(HungrySingleton.getSingleton());
        System.out.println(LazySingleton.getSingleton());
        System.out.println(StaticInnerSingleton.getSingleton());
    }
}

/**
 * 饿汉式单例
 */
class HungrySingleton {
    private HungrySingleton() {
    }

    private static HungrySingleton singleton = new HungrySingleton();

    public static HungrySingleton getSingleton() {
        return singleton;
    }
}

/**
 * 懒汉式单例
 */
class LazySingleton {
    private LazySingleton() {
    }

    private static LazySingleton singleton = null;

    public static synchronized LazySingleton getSingleton() {
        if (singleton == null) {
            singleton = new LazySingleton();
        }
        return singleton;
    }
}


/**
 * 静态内部类实现单例
 */
class StaticInnerSingleton {
    private StaticInnerSingleton() {
    }

    private static StaticInnerSingleton singleton;

    private static class SingletonHandler {
        private static final StaticInnerSingleton singleton = new StaticInnerSingleton();
    }

    public static StaticInnerSingleton getSingleton() {
        return SingletonHandler.singleton;
    }
}