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POPattern for lazy thread-safe singleton instantiation in java
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  1. POPattern for lazy thread-safe singleton instantiation in java
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    copied!<p>the lazy thread-safe singleton instantion is kinda not easy to understand to every coder, so i wanted to create a class in our enterprise framework that would do the job.</p> <p>What do you think about it? Do you see something bad about it? Is there something similar like in Apache Commons? How can i make it better?</p> <p>Supplier.java</p> <pre><code>public interface Supplier&lt;T&gt; { public T get(); } </code></pre> <p>LazyThreadSafeInstantiator.java</p> <pre><code>public class LazyThreadSafeInstantiator&lt;T&gt; implements Supplier&lt;T&gt; { private final Supplier&lt;T&gt; instanceSupplier; private volatile T obj; public LazyThreadSafeInstantiator(Supplier&lt;T&gt; instanceSupplier) { this.instanceSupplier = instanceSupplier; } @Override // http://en.wikipedia.org/wiki/Double-checked_locking public T get() { T result = obj; // Wikipedia: Note the usage of the local variable result which seems unnecessary. For some versions of the Java VM, it will make the code 25% faster and for others, it won't hurt. if (result == null) { synchronized(this) { result = obj; if (result == null) { result = instanceSupplier.get(); obj = result; } } } return result; } } </code></pre> <p>Example usage:</p> <pre><code>public class Singleton1 { private static final Supplier&lt;Singleton1&gt; instanceHolder = new LazyThreadSafeInstantiator&lt;Singleton1&gt;(new Supplier&lt;Singleton1&gt;() { @Override public Singleton1 get() { return new Singleton1(); } }); public Singleton1 instance() { return instanceHolder.get(); } private Singleton1() { System.out.println("Singleton1 instantiated"); } } </code></pre> <p>Thanks</p>
 

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