programming-for-dummies

Figuring Out Programming 23
certain types of programming languages known as scripting languages. (Find
out more about scripting languages in Book I, Chapter 3.)
Book I
Chapter 1
Combining a compiler with an interpreter
to create p-code
Creating separate executable files for each processor can get clumsy and giving
away your source code with an interpreter may be unreasonable, so a third
approach is to compile your program into an intermediate format called bytecode
or pseudocode (often abbreviated as p-code). Unlike compiling source
code directly into machine language, you compile your program into a p-code
file instead.
Getting Started
Programming a
Computer
You can take this p-code file and copy it on any computer. To run a p-code
file, you need a special p-code interpreter, or a virtual machine. The virtual
machine acts like an interpreter and runs the instructions compiled into the
p-code file.
✦ The advantage of p-code is that you can distribute a single p-code version
of your program, which can run on multiple computers.
✦ P-code has a couple disadvantages:
• P-code programs don’t run as fast as programs compiled into
machine language.
• If a computer doesn’t have the right virtual machine installed, it can’t
run your program.
The most popular programming language that uses p-code is Java. After you
write a Java program, you can compile it into a p-code file, which can run on
any computer that has a copy of the Java virtual machine (VM), such as
Windows, Mac OS X, and Linux.
The theory behind p-code is that you write a program once and you can run
it anywhere. The reality is that every operating system has its quirks, so it’s
more common to write a program and be forced to test it on multiple operating
systems. More often than not, a p-code program runs perfectly fine on one
operating system (like Windows) but suffers mysterious problems when running
on another operating system (such as Linux). Languages, such as Java,
are getting better at letting you run the same program on multiple operating
systems without major modifications, but be careful because p-code doesn’t
always work as well as you might think.
Taking the time to understand
Programming is a skill that anyone can acquire. Like any skill, the best way
to understand is to take the time to experiment, make mistakes, and learn
from your failures. Some programmers prefer to spend their time mastering