Java is a high-level, object-oriented programming language.
It has been designed for a general-purpose programming language intended to let application developers write once, run anywhere, meaning that compiled Java code can run on all platforms that support Java without the need for recompilation.
James Gosling, Mike sheridan, and Patrick Naughton initiated the Java language project in June 1991. Gosling designed Java with a C/C++ style syntax that system and application programmers would find familiar.
Sun Microsystems released the first public implementation as Java 1.0 in 1996.
If you write source code with Java, you can reuse compiled byte code on any os platform such as Windows, Mac, or Linux.
Java source code is saved as a form of ".JAVA". It can be compiled from source code to byte code with java.exe program that is included in JDK.
Byte code is only readed by computer, and it has .class extention.