Java was developed by Sun Microsystems in 1995, but it has stood the test of time and remains highly relevant and widely used to this day. So what exactly is Java? Java is a high-level, general-purpose object-oriented programming language.

The following are Java's main features:

• High level and general purpose: Rather than being created to accomplish one very specific task, Java allows us to write computer-readable instructions in an open-ended environment. Because it's not really feasible, or even desirable, for every computer system to have its own specialized programming language, the vast majority of the code is written in high-level, general-purpose languages such as Java.
• Object-oriented: Java is also what we call an object-oriented language. While we won't get into the specifics of objects and classes until a bit later in this book, know for now that objects allow us to define modular entities within our program that make them much more human-readable and much more manageable to create large-scale software projects. A firm grasp of object-oriented concepts is absolutely essential for any modern software developer.
• Platform-independent: Lastly, Java was designed with the intention that it be a write once, run anywhere language. This means if you and I both have systems with Java installed and even if our systems are not normally identical--for example, I'm on a Windows machine and you're on a Mac--a Java program on my machine that I give to you will still run essentially the same on your machine without the need for it to be recompiled.

Traditionally, we would have to recompile a program for every system that it was going to run on because all systems have a different idea of what their machine code should look like. Java circumvents this issue by compiling all Java programs to the same type of interpreted code called bytecode.

A compiled Java program in bytecode can be run by any system in which Java is installed. This is because when we install Java on your system, we also install a Java virtual machine with it that's specific to that system. It is this machine's responsibility to convert the bytecode into the final instructions that head to the processor in that system.

By making it the system's responsibility to do this final conversion, Java has created a write once, run anywhere language where I can hand you a Java program and you can run it on your machine while being fairly certain that it's going to run in the same manner that it did on mine. This impressive level of cross-platform support on a language as powerful as Java has made it one of the software developing world's go-to tools for quite some time.

In today's modern times, Java is used to develop desktop applications, web servers, and client-side web applications. It's the native language of the Android operating system, which operates on Android phones and tablets.

Java has been used to write video games and is sometimes even ported to smaller devices without a traditional operating system. It remains a huge player in today's technical world, and I'm looking forward to learning it with you.