Handout 2–2
Web Design & Development CS-506
- 9 -
Java Virtual Machine & Runtime Environment
Basic Concept
When you write a program in C++ it is known as source code. The C++ compiler
converts this source code into the machine code of underlying system (e.g. Windows) If
you want to run that code on Linux you need to recompile it with a Linux based compiler.
Due to the difference in compilers, sometimes you need to modify your code.
Java has introduced the concept of WORA (write once run anywhere). When you write a
java program it is known as the source code of java. The java compiler does not compile
this source code for any underlying hardware system, rather it compiles it for a software
system known as JVM (This compiled code is known as byte code). We have different
JVMs for different systems (such as JVM for Windows , JVM for Linux etc). When we
run our program the JVM interprets (translates) the compiled program into the language
understood by the underlying system. So we write our code once and the JVM runs it
everywhere according to the underlying system.
This concept is discussed in detail below
Java Compiler javac
Java Byte
Code
JAVA
Source
Code
Java Interpreter
Machine
Code
