Package org.opengrok.indexer.util

Class LazilyInstantiate<T>

java.lang.Object
org.opengrok.indexer.util.LazilyInstantiate<T>
Type Parameters:
T - the type of object that you're trying to lazily instantiate
All Implemented Interfaces:
Supplier<T>
public class LazilyInstantiate<T> extends Object implements Supplier<T>
LazilyInstantiate is a quick class to make lazily instantiating objects easy. All you need to know for working with this class is its two public methods: one static factory for creating the object, and another for initiating the instantiation and retrieval of the object.

Also, another benefit is that it's thread safe, but only blocks when initially instantiating the object. After that, it stops blocking and removes unnecessary checks for whether the object is instantiated.

Here's an example of it being used for implementing a singleton: public class Singleton
{
    private static Supplier<Singleton> instance = LazilyInstantiate.using(() -> new Singleton());
    //other fields

    public static getInstance()
    {
        instance.get();
    }

    //other methods

    private Singleton()
    {
        //contructor stuff
    }
}

So, here are the changes you'll need to apply in your code:

  • Change the type of the lazily instantiated object to a Supplier of that type
  • Have it set to LazilyInstantiate.using() where the argument is () -> <instantiation code> You could also use a method reference, which, for the example above, would be Singleton::new instead of () -> new Singleton()
  • Whatever asks for the object, asks for the Supplier object, then .get()

  • Method Details

    • using

      public static <T> LazilyInstantiate<T> using(Supplier<T> supplier)

    • get

      public T get()
      Executes the using(java.util.function.Supplier) supplier in a thread-safe manner if it has not yet been executed, and keeps the result to provide to every caller of this method.
      Specified by:
      get in interface Supplier<T>
      Returns:
      the result of supplier

    • isActive

      public boolean isActive()
      Gets a value indicating if the instance is active and no longer technically lazy, since get() has been called.