singleton

Singleton

• Famille : Création

Description du patron

Structure

Comportement

Exemple

Démonstration

• Pour compiler le code :
  • lucifer:singleton mosser$ mvn -q clean package
• Pour exécuter la démonstration :
  • lucifer:singleton mosser$ mvn -q exec:java

Code

System.out.println("###\n# Regular usage\n###");
Product reg1 = new Regular();
reg1.doSomething();
Product reg2 = new Regular();
reg2.doSomething();
Product reg3 = new Regular();
reg3.doSomething();
System.out.println("Number of instances created: " + Regular.howManyCreated()+"\n");

System.out.println("\n###\n# Singleton usage\n###");
// Product sing1 = new Unique(); // Does not compile, thanks to the private constructor
Product sing1 = Unique.build();
sing1.doSomething();
Product sing2 = Unique.build();
sing2.doSomething();
Product sing3 = Unique.build();
sing3.doSomething();
System.out.println("Number of instances created: " + Unique.howManyCreated()+"\n");

Trace

###
# Regular usage
###
==>> A new regular product is instantiated  <<==
I am a regular product doing something
==>> A new regular product is instantiated  <<==
I am a regular product doing something
==>> A new regular product is instantiated  <<==
I am a regular product doing something
Number of instances created: 3

###
# Singleton usage
###
==>> A new unique product is instantiated <<==
I am an unique product doing something
I am an unique product doing something
I am an unique product doing something
Number of instances created: 1