Although you can find an online javadoc for Java SE, there is no online version of Java ME API docs on the internet. But you can download an offline version of javadoc and browse it locally.
Here's the walkthrough for MIDP 2.0: (You can do the same for other additional apis or for a newer version of MIDP published in the future.)
- Goto http://java.sun.com/j2me/docs/
- Click on link "MIDP 2.0 Specification (JSR 118)"
- Under Specification, Click on Download
- Hit Accept License Agreement
- Download ZIP file (not the pdf version)
- Unzip file and view files
- Enter folder "midpng-javadoc-final"
- Open Overview.html
- Find link "JavaDoc API Documentation".