The Java Programming Language and the Java Platform

Java is a high-level language and software-only platform. It runs on more than 50 million personal computers and on billions of devices worldwide. 9 million developers have created Java applications in all major industries.

The two main components of the Java platform are the Java Application Programming Interface (API), which is a library of Java command lines and the Java Virtual Machine (JVM) that interprets Java code into machine language. 

The same application can run on multiple platforms
JVM
The API and the JVM make the program independent from the underlying hardware
Java Platform

Learn about the JVM and the APIs

Jump into Java

Code a “Hello World” application in Java.  Follow these step-by-step instructions to quickly create your first application using a text editor in Windows or with NetBeans Integrated Development Environment (IDE). 

Learn Java programming with The Java Tutorials, a comprehensive source for Java language concepts.  Object-oriented and Java programming are explained with graphics and code examples. 

Pick the right tool.  Professionals use NetBeans IDE, an Oracle full-featured Java development software program and JavaFX, a client platform to create and deploy rich Internet applications. Beginners use visual educational tools such as Alice, Greenfoot and BlueJ.  The Young Developers  page summarizes the tools and learning resources for each software tool.

 
Recommended books:

“Core Java, Volume I - Fundamentals (9th edition) by Cay Horstmann and Gary Cornell
“Core Java, Volume II – Advanced Features (9th edition) by Cay Horstmann and Gary Cornell
“Head first Java” by Kathy Sierra and Bert Bates.  2nd edition is Free in eBook version
"Thinking in Java" by Bruce Eckel
Oracle Java Magazine book section