1、单例模式
饿汉模式
优点：执行效率高，性能高，没有任何的锁
缺点：某些情况下，可能会造成内存的浪费
public class MyStaticHungrySingleton { private static final MyStaticHungrySingleton myStaticHungrySingleton; static{ myStaticHungrySingleton = new MyStaticHungrySingleton(); } private MyStaticHungrySingleton(){} public MyStaticHungrySingleton getInstance(){ return myStaticHungrySingleton; } }<br><br>public class MyHungrySingleton {<br> private static final MyHungrySingleton myHungrySingleton = new MyHungrySingleton();<br><br> private MyHungrySingleton(){}<br><br> private MyHungrySingleton getInstance(){<br> return myHungrySingleton;<br> }<br>}
懒汉式单例
优点：节省内存
缺点：性能下降
public class LazySimpleSingletion { private static LazySimpleSingletion instance; private LazySimpleSingletion(){} public synchronized static LazySimpleSingletion getInstance(){ if(instance == null){ instance = new LazySimpleSingletion(); } return instance; } } //性能下降 public class LazyDoubleCheckSingletion { private volatile static LazyDoubleCheckSingletion instance; private LazyDoubleCheckSingletion(){} public static LazyDoubleCheckSingletion getInstance(){ //检查是否要阻塞 if(instance==null){ synchronized (LazyDoubleCheckSingletion.class){ //检查是否要创建实例 if(instance==null){ instance = new LazyDoubleCheckSingletion(); } } } return instance; } } //指令重排序
