jgs CSE 460 Software Analysis and Design Lecture 17: Singleton Dr. Javier Gonzalez-Sanchez [email protected] javiergs.engineering.asu.edu | javiergs.com PERALTA 230U Office Hours: By appointment 

jgs Previously … 

jgs 00010000 Practice 

jgs 00010000 Observer Pattern 

jgs 00010000 Decorator Pattern 

jgs 00010000 Solution: UI + Observer + Decorator 

jgs Let us Continue the Practice 

jgs 00010000 GoF Patterns 

jgs Singleton 

jgs 00010000 Singleton A B 

jgs 00010000 Singleton A B Printer DataBaseConnection UniversityPresident Pacman Logger ControlCenter 

jgs 00010000 Singleton 

jgs 00010000 Singleton class Main { public static void main(String []a){ // Constructor is protected -- cannot use new Singleton s1 = Singleton.getInstance(); Singleton s2 = Singleton.getInstance(); // Test for same instance if (s1 == s2){ // true - Objects are the same instance } } } 

jgs 00010000 Singleton class Singleton{ private static Singleton instance; // Constructor is 'protected' protected Singleton() {} public static Singleton getInstance(){ if (instance == null){ instance = new Singleton(); } return instance; } } 

jgs 00010000 Practice 

jgs 00010000 A Singleton 

jgs 00010000 Add More Objects 

jgs CSE 460 Software Analysis and Design Javier Gonzalez-Sanchez [email protected] Fall 2020 Disclaimer. These slides can only be used as study material for the class CSE460 at ASU. They cannot be distributed or used for another purpose.