[디자인패턴] Singleton

< Eager initialization >

public class Singleton {
    private static final Singleton instance = new Singleton();

    private Singleton() {}

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


< Lazy initialization >

public class SingletonDemo {
        private static volatile SingletonDemo instance = null;

        private SingletonDemo() {       }

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




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출처 : 위키피디아 (http://en.wikipedia.org/wiki/Singleton_pattern)