Unit 1: Introduction to Java

Lesson 1: What is Java?

It's a FREE programming language based on C and C++. It can run as an application on a computer or as an applet in a browser. You cannot make a java program into a .exe file.

Special features:

object oriented (OOP = object oriented programming) (everything is an object)
OOP is not the solution for everything. It is a useful way to program in many situations, but not everything can be easily represented as an object. There may be better ways to program something.
platform independent (a platform is a type of computer / operating system)
automatic memory management (unlike C and C++) with garbage collection
type checking (unlike Javascript)
exception handling to take care of errors properly (this is becoming more widely used)

Why study Java?

1. Look at these three websites. What do you notice?

2. Android uses Java

How does Java work?

There are always two steps: COMPILE, then RUN:

	source code	——► compile	bytecode	——► run	machine code running on CPU
	written using an IDE	compiler (in JDK)		JVM (interpreter) (in JRE)
Filenames:	*Program.java*	*javac.exe*	*Program.class*	*java.exe*

You can write the source code in any editor (as long as it is saved in plain text format) or IDE.
Source code must have the same name as the main class
Source code must end in .java
It is compiled to bytecode by the java compiler (javac.exe)
Bytecode is saved with the extension .class
The bytecode can be put on any operating system and will be run by the Java Virtual Machine for that OS and CPU.

Your first program

Have a look at this set of templates and then write a program to print "Hello World".