java设计模式--单例模式

/**
 * 单例模式：懒汉模式
 * 
 * @author yannic
 *
 */
public class SingleInstance {
    //volatile修饰，禁止指令重拍
    private static volatile SingleInstance singleInstance;

    // 私有化构造器,防止外部的类调用创建新对象
    private SingleInstance() {
    }

    public static SingleInstance getInstance() {
        //double-check：双重检查
        if (singleInstance == null) {
            synchronized (SingleInstance.class) {
                if (singleInstance == null) {
                    singleInstance = new SingleInstance();
                }
            }
        }
        return singleInstance;
    }

}

/**
 * 单例模式：饿汉模式
 * 
 * @author yannic
 *
 */
public class Singleton {
    //类加载时就初始化
    private static final Singleton singleton = new Singleton();
    //私有化构造器
    private Singleton() {
    }

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