Add method summaries as java doc

[feenr]

In a recent commit we enabled checkstyle as a build task. Most of the checkstyle issues were addressed, but validation requiring method summaries was disabled because there were 50-60 methods which needed to be documented.

As an easy task for someone looking to get familiar with this project, it would be nice to have method summaries and re-enabled the checkstyle configuration.

Expected Behavior

Public methods should have javadoc method summaries. Checkstyle validation should make sure this practice is carried forward.

Current Behavior

Most public methods in this project do not have documentation, and the validation is disabled in checkstyle configuration.