java-generator-functions

An implementation of Python-like generator functions in Java. This repository contains a single class, Generator with a method yield(...) which can be used to mimic the behaviour of the yield keyword in Python.

Examples

The following is a simple generator that yields 1 and then 2:

Generator<Integer> simpleGenerator = new Generator<Integer>() {
    public void run() throws InterruptedException {
        yield(1);
        // Some logic here...
        yield(2);
    }
};
for (Integer element : simpleGenerator)
    System.out.println(element);
// Prints "1", then "2".

Infinite generators are also possible:

Generator<Integer> infiniteGenerator = new Generator<Integer>() {
    public void run() throws InterruptedException {
        while (true)
            yield(1);
    }
};

The Generator class lies in package io.herrmann.generator. So you need to import io.herrmann.generator.Generator; in order for the above examples to work.

Usage

This package is hosted as a Maven repository with the following url:

http://dl.bintray.com/filipmalczak/maven

To use it from Maven, add the following to your pom.xml:

<project>
    ...
    <repositories>
        ...
        <repository>
            <id>java-generator-functions</id>
            <url>http://dl.bintray.com/filipmalczak/maven</url>
        </repository>
    </repositories>
    ...
    <dependencies>
        <dependency>
            <groupId>io.herrmann</groupId>
            <artifactId>java-generator-functions</artifactId>
            <version>1.0</version>
        </dependency>
    </dependencies>
</project>

For Gradle:

compile(group: 'io.herrmann', name: 'java-generator-functions', version: '1.0')

Caveats and Performance

The Generator class internally works with a Thread to produce the items. It does ensure that no Threads stay around if the corresponding Generator is no longer used. However:

If too many Generators are created before the JVM gets a chance to garbage collect the old ones, you may encounter OutOfMemoryErrors. This problem most strongly presents itself on OS X where the maximum number of Threads is significantly lower than on other OSs (around 2000).

The performance is obviously not great but not too shabby either. On my machine with a dual core i5 CPU @ 2.67 GHz, 1000 items can be produced in < 0.03s.

Contributing

Contributions and pull requests are welcome. Please ensure that mvn test still passes and add any unit tests as you see fit. Please also follow the same coding conventions, in particular the line limit of 80 characters and the use of tabs instead of spaces.