How to Install Java

Most of the mac users have Java installed in their machines and they are good to go. If you want to check if it is properly installed go to: Test Installation This will show you the Java version.

If it is not installed, You can find the instructions/dowloand pages on Java.com

Java Reference

The lasted Java documentation is at Java doc
Javadoc is a set of HTML pages describing classes, nested classes, interfaces, constructors, methods, and fields.

Each page is devided to three sections: One for Java Packages (the current pakage) , One is to show all the classes in that package, and the main page that shows the selected class information (for example the methods available in that class).
The main information consists of Constructor Summary and Method Summary that shows the format of input and output of that method. That means the parameters of the method, what the method returns,

Eclipse

Eclipse can be found at http://www.eclipse.org

To get started, make a project and add your java files (classes to that project)
To make a project, select new Project, choose "Java Project" and give it a name. Then you could right click at project name and add Java classes to it.