Java设计模式—singleton 单例

整理一下! 
饿汉式单例类

public class SingleManager {

        private SingleManager() {

                System.out.println("Singleton!");
        }

        private static final SingleManager instance = new SingleManager();

        public static SingleManager getInstance() {

                return instance;
        }

        public static void main(String[] args) {
                SingleManager.getInstance();
        }
}

懒汉式单例类 

public class SingleManager {

        private SingleManager() {

                System.out.println("Singleton!");
        }

        private static SingleManager instance = null;

        public static synchronized SingleManager getInstance() {
                if (instance == null) {
                        instance = new SingleManager();
                }
                return instance;
        }

        public static void main(String[] args) {
                SingleManager.getInstance();
        }
}

内部类式单例类 

public class SingleManager {

    private SingleManager(){
            System.out.println("Singleton!");
    }

    static class  SingletonHolder{
            private static SingleManager instance = new SingleManager();
    }

    public static SingleManager getInstance(){

            return SingletonHolder.instance;
    }

    public static void main(String[] args){
            SingleManager.getInstance();
    }
}