1. IB Computer Science II Paul Bui
Introduction to Java
IB Computer Science II
Paul Bui

2. What does a computer look like?
Central
Processing
Unit
(CPU)
Memory

3. What is a computer program?

4. Assembly Language
Also known as machine code/language or low-level language
Example:
ADD R1, R2, R3
SUB R1, R1, 1
MULT R3, R1, R2
Why can’t I run my PC programs on a Mac?!?!?
Different from machine to machine

5. I Hate Tedious Stuff Old school programs
Invention of the high-level language
ADD R1, R2, R3
SUB R1, R1, 1  D = B*(B+C-1)
MULT R4, R1, R2
Waaaay easier to understand

6. Compilers
Translates or converts a high-level language (e.g., Java, C++) to a low-level language
Does other stuff too!
Checks syntax
Optimizations
and more!
One would say, “Yeah, so I compiled my code to an executable or binary”

7. Before Java… Applications or Programs
Operating System (Windows XP, Mac OSX, etc.)
Hardware (CPU + Memory + etc.)

8. How Java Works Java Application or Java Program
Java Runtime Environment or Java Virtual Machine
Operating System (Windows XP, Mac OSX, etc.)
Hardware (CPU + Memory + etc.)

9. What does this mean? Java bytecode (Java’s low-level language)
Java sourcecode (high-level)  Java bytecode (low-level)  assembly
Two different operating systems with the JRE or JVM can run the same Java program

10. Ok, so I want to program now!
//My first Java program!
class HelloWorld{
public static void main(String[] args) {
System.out.println("Hello World!"); }

11. How to Compile and Execute
Open a text editor (gedit, tea, vi, etc.)
Code Code Code
Save file as CLASSNAME.java
Example: HelloWorld.java
Open a terminal
javac HelloWorld.java
java HelloWorld