Treeehouse provides an app for both iOS and Android that are easy to use.

The Java courses take you through building various projects, such as command line programs and a pomodoro timer app.

Treehouse offers a learning track for Java, which is a collection of some of their Java courses that gradually increase in difficulty.

When starting with a new language, it's not always easy to figure out what to learn next. Learning tracks solve that problem by following an intuitive progression.