Lazy4J

A generic Lazy class in java

What is it?

A wrapper for a Supplier function that evaluates it lazily when it is first needed, remembering the result so the wrapped supplier does not get called again.
Lazy wraps the Supplier functional interface.

Why?

This is often recurring functionality that should have been provided out of the box by the JDK when lambda's were introduced in Java 8.

Fortunately, it's not very difficult to create, so that's what we did.

Example

A small example of how this class can be used:

public class Example {
    private final Lazy<Expensive> expensive = Lazy.lazy(Expensive::create);
}

This declares a lazy expensive variable without creating an expensive object yet.
Only when get() is called for the first time, the Expensive.create() method is called.
All subsequent invocations will return the same instance of Expensive.

Lazy provides the following methods:

isAvailable returning whether the lazy value is already available.
map applies a function on the lazy result.
flatMap applies a function that itself returns a supplier.
ifAvailable runs a function only if the lazy value is already available.

Please refer to the Lazy class documentation for full descriptions.

Getting the class

Add the following dependency to your project or download it directly from github:

Maven

<dependency>
    <groupId>nl.talsmasoftware</groupId>
    <artifactId>lazy4j</artifactId>
    <version>[see maven badge]</version>
</dependency>

Gradle

compile 'nl.talsmasoftware:lazy4j:[see maven-central badge]'

Scala

libraryDependencies += "nl.talsmasoftware" % "lazy4j" % "[see maven-central badge]"

License

Apache 2.0 license

talsma-ict/lazy4j