Singleton[OOD]

Singleton

guarantee a class only have one instance, provide global access to the instance

Multiple threading

S1

public class Singleton {

private final Singleton instance;

private Singleton() {

// dosth

};

public static synchronized Singleton getInstance() {

if (instance == null) {

instance = new Singleton();

}

return instance;

};

}

Singleton s1 = Singleton.getInstance();

Singleton s2 = Singleton.getInstance();

how to handle the critical section

option1: add synchronized keyword

option2: design

option3: double check

S2:

public class Singleton {

private static final Singleton INSTANCE = new Singleton();

private Singleton() {

// do sth;

}

public static Singleton getInstance() {

return INSTANCE;

}

}