According to Wikipedia, Java is a general-purpose computer programming language that is
concurrent , class-based , object-oriented , and specifically designed to let application developers " write once, run anywhere"(WORA), meaning that compiled Java code can run on all platforms that support Java without the need for recompilation.

Java was originally developed by James Gosling at Sun Microsystems (which has since been
acquired by Oracle Corporation) and released in 1995.

The latest version is Java 8 which is the only version currently supported for free by Oracle, although earlier versions are supported both by Oracle and other companies on a commercial basis.

There were five primary goals in the creation of the Java language:
1. It must be "simple, object-oriented, and familiar".
2. It must be "robust and secure".
3. It must be "architecture-neutral and portable".
4. It must execute with "high performance".
5. It must be "interpreted, threaded, and dynamic".

To learn Java, for hardware, you must have a good computer with a sizeable amount of RAM(minimum of 64MB) and a disk space above 200MB.

For software, you will need:

- A compatible operating system (Windows, Linux, Mac OS etc)

-Java Development Kit ( JDK 8 recommended)

-Eclipse/Netbeans (This is recommended, but in actuality, any text editor will do)

If you have all that, you are good to go.