java单例模式

(1),懒汉式单例

优点: 第一次调用才初始化,避免浪费内存. 缺点: 必须加synchronized才能保证单例,但加锁会影响效率.

public class Student{ private static Student student; private Student(){} public static synchronized Student getInstance(){ if(student=null){ student=new Student(); } return student; } }

(2),饿汉式单例

优点: 没有加锁,执行效率会提高. 缺点: 类加载时就初始化,浪费内存.

public class Student{ public static final Student stu=new Student(); private Student(){} public static Student getInstance(){ return stu; } }

(3),登记式单例

内部类只有在外部类被调用才加载;又不用加锁,此模式有上述两种模式的优点,屏蔽了它们的缺点,才是最好的单例模式.

public class Student{ private Student(){} public static Student createObj(){ return Holder.stu; } private static class Holder{ private static final Student stu=new Student(); } }