04-12-2012, 01:16 PM
Introduction to Java
Introduction to Java.ppt (Size: 40.5 KB / Downloads: 216)
Introduction
Present the syntax of Java
Introduce the Java API
Demonstrate how to build
stand-alone Java programs
Java applets, which run within browsers e.g. Netscape
Example programs
Why Java?
It’s the current “hot” language
It’s almost entirely object-oriented
It has a vast library of predefined objects and operations
It’s more platform independent
this makes it great for Web programming
It’s more secure
It isn’t C++
Applets, Servlets and Applications
An applet is designed to be embedded in a Web page, and run by a browser
Applets run in a sandbox with numerous restrictions; for example, they can’t read files and then use the network
A servlet is designed to be run by a web server
An application is a conventional program
Java Virtual Machine
The .class files generated by the compiler are not executable binaries
so Java combines compilation and interpretation
Instead, they contain “byte-codes” to be executed by the Java Virtual Machine
other languages have done this, e.g. UCSD Pascal
This approach provides platform independence, and greater security
Java isn't C!
In C, almost everything is in functions
In Java, almost everything is in classes
There is often only one class per file
There must be only one public class per file
The file name must be the same as the name of that public class, but with a .java extension
What is a class?
Early languages had only arrays
all elements had to be of the same type
Then languages introduced structures (called records, or structs)
allowed different data types to be grouped
Then Abstract Data Types (ADTs) became popular
grouped operations along with the data
Name conventions
Java is case-sensitive; maxval, maxVal, and MaxVal are three different names
Class names begin with a capital letter
All other names begin with a lowercase letter
Subsequent words are capitalized: theBigOne
Underscores are not used in names
These are very strong conventions!