Create only one object for a class and reuse same object

Question

I want to create only one object of an class and reuse the same object over and over again. Is there any efficient way to do this.

How can I do this?

What exactly are you trying to do? Do you have an example class? — cowls, Jan 03 '13 at 08:42
@AjayGopalShrestha if the question has been answered to your satisfaction, please mark the appropriate answer as accepted. — Steve, Jan 03 '13 at 08:59

Steve · Accepted Answer · 2013-01-03T08:52:09.143

11

public final class MySingleton {
    private static volatile MySingleton instance;

    private MySingleton() {
        // TODO: Initialize
        // ...
    }

    /**
      * Get the only instance of this class.
      *
      * @return the single instance.
      */
    public static MySingleton getInstance() {
        if (instance == null) {
            synchronized (MySingleton.class) {
                if (instance == null) {
                    instance = new MySingleton();
                }
            }
        }
        return instance;
    }
}

edited Jan 03 '13 at 08:52

answered Jan 03 '13 at 08:45

Steve

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Ok, that was just embarrassing. – Steve Jan 03 '13 at 08:49
There's no need to make the entire method synchronized. See the example here: http://en.wikipedia.org/wiki/Singleton_pattern#Lazy_initialization – Sean Patrick Floyd Jan 03 '13 at 08:49
Is it advisable or overkill to mark the class as final so it cannot be extended? – shuttsy Jan 03 '13 at 08:50
Updated with recommendations here. It's a tad complex for a beginner now, though. – Steve Jan 03 '13 at 08:53
3

@AjayGopalShrestha Think twice before going for a singleton. [They are evil in most situations](http://stackoverflow.com/questions/1300655/whats-alternative-to-singleton). – assylias Jan 03 '13 at 08:53
Or you could use an `enum` with three lines. See my answer. – Peter Lawrey Jan 03 '13 at 10:31

score 2 · Answer 2 · edited May 23 '17 at 12:02

2

This is generally implemented with the Singleton pattern but the situations where it is actually required are quite rare and this is not an innocuous decision.

You should consider alternative solutions before making a decision.

This other post about why static variables can be evil is also an interesting read (a singleton is a static variable).

edited May 23 '17 at 12:02

Community

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answered Jan 03 '13 at 08:43

assylias

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score 2 · Answer 3 · answered Jan 03 '13 at 10:30

The simplest way to create a class with one one instance is to use an enum

public enum Singleton {
    INSTANCE
}

You can compare this with Steve Taylor's answer to see how much simple it is than alternatives.

BTW: I would only suggest you use stateless singletons. If you want stateful singletons you are better off using dependency injection.

score 0 · Answer 4 · edited May 23 '17 at 12:09

0

That would be the Singleton pattern - basically you prevent construction with a private constructor and "get" the instance with a static synchronized getter that will create the single instance, if it doesn't exist already.

Cheers,

edited May 23 '17 at 12:09

Community

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answered Jan 03 '13 at 08:43

Anders R. Bystrup

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score 0 · Answer 5 · answered Jan 03 '13 at 08:43

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There is a design pattern called Singleton. If you implement it, you will get to what you need.

Take a look at this to see different ways to implement it.

answered Jan 03 '13 at 08:43

Dan D.

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score 0 · Answer 6 · answered Jan 03 '13 at 08:43

0

Yes. Its called a Singleton class. You create one and only instance and use it throughout your code.

answered Jan 03 '13 at 08:43

giorashc

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score 0 · Answer 7 · answered Jan 03 '13 at 08:43

You are looking for the Singleton pattern. Read the wikipedia article and you will find examples of how it can be implemented in Java.

Perhaps you'd also care to learn more about Design Patterns, then I'd suggest you read the book "Head First Design Patterns" or the original Design Patterns book by Erich Gamma et al (the former provides Java examples, the latter doesn't)

score 0 · Answer 8 · answered Jan 03 '13 at 08:44

0

What you are looking for is the Singleton Pattern.

answered Jan 03 '13 at 08:44

Jean Logeart

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Create only one object for a class and reuse same object

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