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POSingleton with Arguments in Java
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copied!<p>I was reading the Singleton article on Wikipedia and I came across this example:</p> <pre><code>public class Singleton { // Private constructor prevents instantiation from other classes private Singleton() {} /** * SingletonHolder is loaded on the first execution of Singleton.getInstance() * or the first access to SingletonHolder.INSTANCE, not before. */ private static class SingletonHolder { private static final Singleton INSTANCE = new Singleton(); } public static Singleton getInstance() { return SingletonHolder.INSTANCE; } } </code></pre> <p>While I really like the way this Singleton behaves, I can't see how to adapt it to incorporate arguments to the constructor. What is the preferred way to do this in Java? Would I have to do something like this?</p> <pre><code>public class Singleton { private static Singleton singleton = null; private final int x; private Singleton(int x) { this.x = x; } public synchronized static Singleton getInstance(int x) { if(singleton == null) singleton = new Singleton(x); return singleton; } } </code></pre> <p>Thanks!</p> <hr> <p>Edit: I think I have started a storm of controversy with my desire to use Singleton. Let me explain my motivation and hopefully someone can suggest a better idea. I am using a grid computing framework to execute tasks in parallel. In general, I have something like this:</p> <pre><code>// AbstractTask implements Serializable public class Task extends AbstractTask { private final ReferenceToReallyBigObject object; public Task(ReferenceToReallyBigObject object) { this.object = object; } public void run() { // Do some stuff with the object (which is immutable). } } </code></pre> <p>What happens is that even though I merely pass a reference to my data to all of the tasks, when the tasks are serialized, the data gets copied over and over. What I want to do is share the object among all of the tasks. Naturally, I might modify the class like so:</p> <pre><code>// AbstractTask implements Serializable public class Task extends AbstractTask { private static ReferenceToReallyBigObject object = null; private final String filePath; public Task(String filePath) { this.filePath = filePath; } public void run() { synchronized(this) { if(object == null) { ObjectReader reader = new ObjectReader(filePath); object = reader.read(); } } // Do some stuff with the object (which is immutable). } } </code></pre> <p>As you can see, even here I have the issue that passing a different file path means nothing after the first one is passed. This is why I like the idea for a <em>store</em> which was posted in the answers. Anyhow, rather than including the logic for loading the file in the run method, I wanted to abstract this logic into a Singleton class. I will not provide yet another example, but I hope you get the idea. Please let me hear your ideas for a more elegant way to accomplish what I am trying to do. Thank you again!</p>

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