java 设计模式之单例模式的7中写发

1.饿汉式（静态参数）

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

2.饿汉式（静态代码块）

class Student { private static Student instance = null; static { instance = new Student(); } private Student (){} public static Student getInstance() { return instance; } }

3.懒汉式（线程不安全）

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

4.懒汉式（线程安全）

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

5.静态内部类

class Student { private static class StudentHolder { private static final Student INSTANCE = new Student(); } private Student (){} public static final Student getInstance() { return StudentHolder.INSTANCE; } }

6.枚举

enum Student { INSTANCE; }

7.双重校验锁

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