設計模式-（單例模式）

2019-11-06 07:18:15

字體：大中小

來源：轉載

供稿：網友

單例設計模式概述?單例模式就是要確保類在內存中只有一個對象，該實例必須自動創建，并且對外提供。優點?在系統內存中只存在一個對象，因此可以節約系統資源，對于一些需要頻繁創建和銷毀的對象單例模式無疑可以提高系統的性能。缺點?沒有抽象層，因此擴展很難。?職責過重，在一定程序上違背了單一職責1.餓漢式代碼：//學生類public class Student { // 構造私有 PRivate Student() { } private static Student s = new Student(); public static Student getStudent() { return s; }}//測試類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.懶漢式代碼//老師類public class Teacher { private Teacher() { } private static Teacher t = null; public synchronized static Teacher getTeacher() { if (t == null) { t = new Teacher(); } return t; }}//測試類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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