Tools all in place for programming: computer, carbs, caffeine

To program in Java (not JavaScript, a similar but different language), you need a "compiler", a program to convert Java source code to bytecode. In the old days, the only option was Sun's Java Development Kit; but now you have many options, including the GNU project's gcj which creates class files or native executables, and jikes, IBM's open source contribution. You also will need a Java virtual machine, which is a "machine within a machine" which understands Java bytecodes and translates them into machine language on the target processor. There are many available, but you can never go wrong with the javac compiler and java JRE virtual machine included with Sun's Java standard edition.

[edit] Steps

Visit Sun's J2SE page and download the correct package for your platform: typically Windows, Linux, or Solaris. Macintosh users will find they already have the J2SE installed. For maximum portability, it may be better to get an older edition; not all your potential users will have the latest JVM installed. Alternatively, use an open-source or other third-party compiler such as gcj or jikes, and compile to a native executable or run it with the Java JRE.
Learn to use a basic, "clean" editor like Notepad, vi, or emacs. These don't taint your program source with formatting information as does, for example, Microsoft Word. Whatever editor you use, it must have the option to save as "plain text".
Learn the basic edit-compile-test cycle:
1. Create or edit the program source file(s).
2. Compile to .class files.
3. Run the program with the java executable, or as an applet in a browser. If the functionality isn't correct, or you want to add more features, start again at step 1.
If you can afford it, buy a good book about Java programming and carefully read the beginning. With this language, the beginning is more difficult than later steps.
Check out sites such as Cksstudios.com, Javacooperation, Cokeandcode and Sun's website for resources/tutorials.
Read up and follow a Java tutorial (one of the first recommended tutorials could be tutorial on collections).
For specific info on the classes, methods, and variables, visit Sun's API
If you face any problems, always try a web search. There are a lot of good articles about Java on the web.

[edit] Tips

Practice makes perfect.
After you master the basics, try to join the existing open source project and work together with other people. From the view point of learning, this is more efficient than to develop something large and complex by yourself.
Keep your code organized and add lots of comments for easy reading, remembering, and updating.
Unnecessarily long methods (the Java name for subroutines) are looked down upon since they make your code hard to read and difficult to update; learn to factor your code into small, precise modules that do one thing well.
Don't use "magic numbers" if you can help it. Magic numbers are numbers and values that are distributed through your code when they should be defined as a variable, so they can be reused, and explained in a comment so what they represent can be understood. This makes code easier to maintain and update.
Download and install an IDE (Integrated Development Environment). For example: NetBeans or Eclipse (open source). This will help speed up the edit-compile-test cycle, at the expense of extra overhead, having to learn a new tool, and limited functionality. Another option is a text-based tool such as GNU Make or Apache Ant, which gives you full control over the process.
Master JUnit and write automatic tests that check the consistency of your program. Most serious projects do this.
Go through the API provided with the SDK. Make a habit of reading the description of the methods and classes. This will help you remember the method or class used the next time you need it.
Learn technologies in which java is strong: network communication, database connection, web development and others.
After you get some experience, try to get official programmer certification from Sun Microsystems itself. This is a lot more serious than any other certification you can get from the third parties.

[edit] Warnings

It is usually not necessary to pay for Java courses that may be very expensive and offer little value. Unless you want to learn something specific, it is frequently better just to do more programming yourself, and learn from other people's open-source programs.