Design Patterns and Best Practices in Java

Lock-free thread-safe singleton

One of the best implementations of the singleton pattern in Java relies on the fact that a class is loaded a single time. By instantiating the static member directly when declared, we make sure that we have a single instance of the class. This implementation avoids locking mechanisms and additional checking to see whether the instance has already been created:

public class LockFreeSingleton{  private static final LockFreeSingleton instance = new   LockFreeSingleton();  private LockFreeSingleton()  {    System.out.println("Singleton is Instantiated.");   }  public static synchronized LockFreeSingleton getInstance()  {    return instance;  }  public void doSomething()  {    System.out.println("Something is Done.");  }}