Android Java 8 Stream API Example

Demo app of using Java 8 features with Retrolambda and Lightweight-Stream-API.

Features:

• () -> lambda expression

  findViewById(R.id.go).setOnClickListener(v -> {
     final int index = mActionSpinner.getSelectedItemPosition();
     if (index != Spinner.INVALID_POSITION) {
         action(actions[index]);
     }
  });

• Method::references

  int cmp = Objects.compare(word, other.word, String::compareToIgnoreCase);

• Stream.API()

  return Stream.of(lines)
       .map(str -> str.split("\t"))
       .filter(arr -> arr.length == 2)
       .map(arr -> new Word(arr[0], arr[1]))
       .collect(Collectors.toList());

• switch for "string"

  switch (action) {
      case "filter 1":
          // Filter one word
          stream = stream.filter(p -> p.getWord().split(" ").length == 1);
          break;
      case "filter 2+":
          // Filter two and more words
          stream = stream.filter(p -> p.getWord().split(" ").length >= 2);
          break;
      // ...
  }

• try(with-resources) {}

  final List<String> lines = new ArrayList<>();
  try (final InputStream is = context.getAssets().open("words.txt");
       final InputStreamReader isr = new InputStreamReader(is, "UTF-8");
       final BufferedReader reader = new BufferedReader(isr)) {
      String line;
      while ( (line = reader.readLine()) != null ) {
          lines.add(line);
      }
  }

• Objects (from Java 7)

  @Override
  public boolean equals(Object o) {
      // ...
      final Word other = (Word) o;
      return Objects.equals(translate, other.translate) &&
             Objects.equals(word, other.word);
  }
  
  @Override
  public int hashCode() {
      return Objects.hash(word, translate);
  }

• try { Exceptional } catch (functional try/catch)

  return Exceptional.of(() -> {
      final InputStream is = context.getAssets().open("words.txt");
      // ... operations which throws Exception ...
      return lines;
  }).ifException(e -> Log.e("Java 8 Example", "Utils.readWords", e))
    .getOrElse(new ArrayList<>());

Links

Demo app: Java8StreamExample.apk

Blog (Russian): Java 8 в Android со Stream API и лямбдами

Retrolambda: https://github.com/orfjackal/retrolambda

Lightweight-Stream-API: https://github.com/aNNiMON/Lightweight-Stream-API

Screenshots