Here is an interesting online tutorial that lets you write and execute basic code in the browser:
http://www.tutorialspoint.com/java/index.htm. As you read through you'll see some sample code and a "try it" button. While in "try it" mode , you are able to change the code.
This may be a good way for someone to get started without being overwhelmed by the JDK and IDE installation. Although that would eventually be needed.