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Java 8 Support

Lambdas and many other features will soon be available in Codename One!
Java 8 Support

Java 8 Support

When we introduced Codename One initially we limited the API to CLDC level which is roughly a subset of Java 1.3, we then added support for a subset of Java 5 and we are now adding Java 8 language features!
Thanks to some work from Steve and the great work done by the guys from the Retro Lambda project we were able to add compatibility to the major Java 8 features, most notably lambda expressions. This is highly experimental and some features might not work but so far it seems things are functioning rather smoothly.

Note that this feature will only be available with the next plugin update and isn't online right now...
The main motivation for doing this is in reducing a lot of the boilerplate code you would normally get when writing Codename One code, e.g. currently we write something like:

button.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {"Event Happened", "You pressed a button", "OK", null);

Whereas lambdas allow us to write this:

button.addActionListener((e) -> {"Event Happened", "You pressed a button", "OK", null);

Technically both are practically identical!
This can be applied across the board e.g.:

Display.getInstance().callSerially(() -> {
    // this code executes on the EDT....

This won't be the default until we are confident that this is stable enough, with an upcoming plugin update you will have an option to create a Java 8 project instead of a Java 5 project. You could also convert existing projects to Java 8 but that will require some effort:

  1. Make sure you have Java 8 installed and that your IDE is running under Java 8
  2. Change all "source" and "target" values for Javac calls in build.xml from 1.5 to 1.8.
  3. Update the IDE build settings for the project (in the project properties menu) to use Java 8 source level
  4. Add the build hint java.version=8
  5. Update CLDC11.jar to the latest version using the Update Client Libs button in the project preferences

The post mostly covered lambdas but other newer Java features such as String based switch cases (from Java 7) try with resources etc. should work just fine however we didn't do enough tests for the various features on all the platforms (hence the beta moniker).
Try with resources is pretty cool e.g. you can do something like:

try(InputStream is = Display.getInstance().getResourceAsStream(getClass(), "/myFile")) {
    // work with file
} catch(IOException err) {"Error", "Exception accessing the resource", "OK", null);

Which doesn't seem like much until you realize that this really replaced this code:

InputStream is = null; 
try {
    is = Display.getInstance().getResourceAsStream(getClass(), "/myFile");
    // work with file
} catch(IOException err) {"Error", "Exception accessing the resource", "OK", null);
} finally {
    if(is != null) {
       try {
       } catch(IOException err) {}

Just to be fair, this code can be slightly more concise in the finalizer block with Codename One's Util.cleanup(is) method...

One feature of Java 8 that isn't supported at the moment is streams. While they would be nice to have they probably won't be as helpful as the other features in a mobile environment and won't provide performance benefits in these cases. We might add them at a future date if there is demand for that.

Notice that Java 8 support was mostly tested with Android, iOS & the desktop port. It should work well with most modern ports but might have issues in platforms such as J2ME/RIM where even the Java 5 compatibility is flaky.
The image in the title of this post is from this Takipi blog which is pretty relevant to the subject of this post.

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Posted by Shai Almog

Shai is the co-founder of Codename One. He's been a professional programmer for over 25 years. During that time he has worked with dozens of companies including Sun Microsystems.
For more follow Shai on Twitter & github.