Java 写一个线程安全的单例模式(饱汉/饿汉）

饿汉单例

public class Singleton {

	private static Singleton singleton = new Singleton();

	private Singleton() {}

	public static Singleton createInstance() {
		return singleton;
	}
}

饱汉单例

public class Singleton {

	private static volatile Singleton baoHan;

	private Singleton() {
	}

	// double check 双重判断检查锁
	public static Singleton createInstance() {
		if (singleton == null) {
			synchronized (Singleton.class) {
				if (singleton == null) {
					singleton = new Singleton();
				}
			}
		}
		return singleton;
	}
}