My travels with Modern Java in Action

Community Journals & Book Clubs
4

Slap bang in the middle of Chapter 5 already which talks about the Stream API and lovin’ it …
… but I’m getting ahead of myself.

The big change for long time Java programmers is the jump to Java 8. Quite literally it is the ability switch from coding in OO to coding in FP. When written well, Java8 code looks quite different to its previous versions.
Here is a very simple example.

Pre Java 8

Using a for loop to iterate a list of String objects.
This is known as external iteration.

public String findWordInList(String wordToFind, List<String> words) {
   for (String word: words) {
       if (word.equals(wordToFind)) {
          return word; 
       }
   }
   return "";
}

Java 8

The same as above but using filter() & findFirst() from the StreamAPI and a lambda predicate. This is known as internal iteration.

public String findWordInList(String word, List<String>) {
   return words.stream()
      .filter(w -> w.equals(wordToFind))
      .findFirst()
      .orElse("");
}

The advantage of internal iteration is that the Stream library can choose a data representation and implementation of parallelism.

To use parallelism you just need to rewrite your code as follows:

public String findWordInList(String word, List<String>) {
   return words.parallelStream()
      .filter(w -> w.equals(wordToFind))
      .findFirst()
      .orElse("");
}

When I see a for statement in code at work these days I experience something akin to being asked to believe that Harry Potter is 14 years old in Harry Potter and the Deathly Hollows.

to be continued …

3 Likes