Design Pattern: Singleton

2013-05-22 146 words One minute

Contents

Singleton pattern ensures that there is only one instance of a class is created in JVM. It is used to provide global point of access to the object.

###Implementation example: Lazy initialization

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public class Singleton {
    private static Singleton instance;

    private Singleton() {
    }

    public static Singleton getInstance() {
        if (instance == null)
            instance = new Singleton();
        return instance;
    }
}

###Implementation example: Eager initialization

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public class Singleton {
    private static Singleton instance = new Singleton()

    private Singleton(){
    }

    public static Singleton getInstance(){
        return instance;
    }
}

In the second implementation, the Singleton instance is instantiated when the class is loaded, while in the first implementation, the instance is not instantiated until it is acturally needed, but the first implementation is not thread safe.