Simon Baars

Notepad++ is insanely simplistic. It doesn't help much with the coding, as it doesn't have stuff like auto-completion. Atom is a great editor for pretty much any language. It has a plugin ide-java to support Java programming. When starting with Java, I would recommend it. But, when becoming even a bit better in the language, I would suggest a more mature IDE like IntelliJ or Eclipse. The refactoring and code manipulation tools make it a lot quicker to program. Only when getting started it might be a bit too much to both learn a language AND learn an IDE. So Atom might be better to get started.