Stream API with Java 6/7 and Android

Java 8 has the new fancy and powerful Streams API but in the Android development world we are still stuck somewhere between Java 6 and 7 and can’t use the Streams API. So there are two ways to solve this:

1. Use Kotlin ;)
2. Use the StreamSupport Library

The StreamSupport Library is a backport of the Java 8 java.util.function (functional interfaces) and java.util.stream (streams) API for users of Java 6 or 7. The Project is hosted at Sourceforge and can easily added to an Android project with gradle. The mvnrepository Link.

compile 'net.sourceforge.streamsupport:streamsupport:1.4.2'

Streams in Java 8

In Java 8 we can easily call stream() on any collection that supports the Stream API. After that call there are many ways to use the stream features. I can recommend this helpful Cheat Sheet: Java 8 Streams Cheat Sheet

Streams with the StreamSupport Library

To use the stream feature with the Library we can not easily call stream() on any collection like in Java 8. We must call StreamSupport.stream(@NotNull java.util.Collection<? extends T> c). But after that call we can use the same functionalities like in the Java Streams API! So we can easily transfer the knowledge from Java 8 Streams to the StreamSupport Library.

Some simple examples

Attention: I’m also using retrolamda. Like StreamSupport it’s a backport of the Lamdba Feature from Java 8. Thats why I can use arrows in my code ;)

The model:

public class Person {
  private String name;
  private int    age;
  private int    zipCode;
  //...getter and setters
}

We want alle persons with age > 21:

private ArrayList<Person> getPersonsOlderThan21(List<Person> persons) {
  return StreamSupport.stream(persons)
    .filter(person -> person.getAge() > 21)
    .collect(Collectors.toCollection(ArrayList::new));
}

With Collectors.toCollection(ArrayList::new) we want to save the result as ArrayList.

Now all persons starting with an “A” in the name:

private List<Person> getPersonsStartingWithAnA(List<Person> persons) {
 return StreamSupport.stream(persons).filter(person ->
  person.getName().startsWith("A")).collect(Collectors.toList());
}

For a List as an Output we call .collect(Collectors.toList()) at the end.

Also we can edit a List. Every Person should be one year older:

private void oneYearOlder() {
  List<Person> persons = new ArrayList<>();
  //code to fill in some datat
  //make each person one year older:
  StreamSupport.stream(persons).forEach(person -> 
    person.setAge(person.getAge() + 1));
  //now each person is one year older
}

Many more examples can be found in other Java 8 Streams Tutorials. I just wanted to show you how we can use Java 8 Streams with Java 6/7 and Android.