设计模式-（单例模式）

2019-11-06 07:18:15

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单例设计模式概述•单例模式就是要确保类在内存中只有一个对象，该实例必须自动创建，并且对外提供。优点•在系统内存中只存在一个对象，因此可以节约系统资源，对于一些需要频繁创建和销毁的对象单例模式无疑可以提高系统的性能。缺点•没有抽象层，因此扩展很难。•职责过重，在一定程序上违背了单一职责1.饿汉式代码：//学生类public class Student { // 构造私有 PRivate Student() { } private static Student s = new Student(); public static Student getStudent() { return s; }}//测试类public class StudentDemo { public static void main(String[] args) { Student s1 = Student.getStudent(); Student s2 = Student.getStudent(); System.out.println(s1 == s2); System.out.println(s1); // null，cn.itcast_03.Student@175078b System.out.println(s2);// null，cn.itcast_03.Student@175078b }}2.懒汉式代码//老师类public class Teacher { private Teacher() { } private static Teacher t = null; public synchronized static Teacher getTeacher() { if (t == null) { t = new Teacher(); } return t; }}//测试类public class TeacherDemo { public static void main(String[] args) { Teacher t1 = Teacher.getTeacher(); Teacher t2 = Teacher.getTeacher(); System.out.println(t1 == t2); System.out.println(t1); // cn.itcast_03.Teacher@175078b System.out.println(t2);// cn.itcast_03.Teacher@175078b }}

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