Netbeans and Eclipse are the most popular IDEs for Java. I do appologize that I can't give any reasons as why you should choose either, as I don't like IDEs.
I have to agree with NormR1. Just get the Java Compiler (javac) and use a program like Notepad++ (Windows), or GEdit (Linux). I can't say about Mac as I don't currently own one.
I think I should explain why I don't like IDEs. First off, I like control. IDEs like to do things for you, but that means I don't have much control over my own code!
Secondly, errors. When I used an IDE for Java it would not even let me run the code because it said it had errors. I could compile it with javac and it would work just fine. But the IDE (I don't remember which one) wouldn't let me for some reason (also lack of control).
Thirdly, understanding. IDEs do things behind the scenes. I like to refer to it as IDE "magic". The more "magic" some program does for me, the less I understand about it (again, it's my own code!).
And finally, simplicity. I'm a simplicity fanatic! If something can do the same job with much less complexity, than I'm all over it. With an IDE you have a million buttons, a million features and a million "magic tricks". Without an IDE you have a Text Editor and a Console window. Simple.
It is a little more typing (javac name.java) per compile, but I've found it to be way beyond worth it. I spend more time coding and less time search IDE errors and solutions. I've given you my reasons, but you may need to see for yourself. Check out the two IDEs I mentioned above if need be and above all else: have fun. :)
At the university im at the first time we ever coded java was in JEdit . Its simple and you don't have to fumble with compiling in command prompt (which honestly when writing really simple programs can be the hardest part, at least i had a lot of trouble with it for some reason.!). We did however quickly switch to eclipse, just because it got so much more utility and eases your coding a lot.
Best IDE? There is none
Most populare? There are few
Most suitable? There is more of them
Started with Notepad and command line so I can get exposed to compile process and all the warning and error messages you may see from it.
Moved on to JCreator to help me with typos etc (no autosuggest used).
Moved on NetBeans becuase of the variety and complexity of projects.
Briefly stopped at Eclipse, but found it unfriendly (at that time there was bad support for JME, now every other day I hear about issues with Maven).
At the end setled for IntelliJ and love it (there are few glitches, but nothing cache clean on re-open project wouldn't solve)