Java is a programming language. It is actually known as a high level programming language because it is closer to natural language than the native instruction set of any real computer.
Since Java is a high level programming language, programs that are written in Java must be translated into a machine language before it can be executed. The program that does this translation is called a compiler.
The machine language that the Java compiler translates to is the Java Virtual Machine language. This language has the odd name "Java byte codes." The Java Virtual Machine (JVM) is not a real computer, but rather just a virtual computer. So the translated byte codes program cannot be executed by any real computer. Instead the Java Virtual (JVM) is really just a program that itself is available in the actual machine language of virtually every computer in the world. This JVM interprets the byte codes and carries out this program as if it (the JVM) were a real computer carrying out instructions. This is somewhat complicated, but this is what makes JVM platform independent.
BlueJ is a special program that allows students to write, compile, and execute Java programs. It has a few main parts:
Read about BlueJ here: http://www.bluej.org/
Download BlueJ here:
http://www.bluej.org/download/download.html
A number of components must be downloaded from the Sun site (the developers and keepers of the Java language). The SDK contains a Java Virtual Machine program and a Java compiler for translating programs into the Java Virtual Machine byte codes format. BlueJ must have the SDK installed in order to work.
One confusing thing is that Sun keeps changing the names of its products. Even though it is the SDK that you need to download, Sun seems to be using "Java 2 Platform Standard Edition" as the name now, or J2SE. If you go to
you should be able to obtain the version of the SDK (J2SE) you need. For compiling Java programs, you will need the entire J2SE, not just the Java Runtime Environment (JRE). The J2SE includes the Java compiler whereas the JRE does not.
You will need to