Design patterns

singleton:

the singleton pattern is a design pattern that restricts the instantiation of a class to one object. It is used when managing access to shared resource. examples: a print spooler, manage a connection to a database. Lazy initialization:

public class SingletonDemo { private static SingletonDemo instance = null; private SingletonDemo() { }

public static synchronized SingletonDemo getInstance() {
    if (instance == null) {
        instance = new SingletonDemo();
    }

    return instance;
}

}

Eager initialization:

public class Singleton { private static final Singleton INSTANCE = new Singleton();

private Singleton() {}

public static Singleton getInstance() {
    return INSTANCE;
}

}