CMSC 202

Computer Science II for Majors

Object-Oriented Programming

Aug 24, 2007 2

Instructors

Mr. Dennis FreySections 0101 – 0105Tues/Thurs 10:00am – 11:15amLH 4 (ACIV)

Mr. Sa’ad RaoufSections 0201 - 0205Mon/Wed 5:30pm – 6:45pmLH 2 (CHEM)

Aug 24, 2007 3

Course Co-ordination

All sections are assigned the same projects All sections are assigned the same labs All sections get the same lecture material, but

exams are different. You must take the exam given by your instructor

Aug 24, 2007 4

What is CMSC 202?

CMSC 202 is an introduction to Object-Oriented programming using the Java programming language

Course websitewww.cs.umbc.edu/courses/undergraduate/202/fall07

Aug 24, 2007 5

Eclipse

An integrated development environment (IDE) for writing Java programs

Free download for your PC See course “Resources” page

Available in all OIT labs around campus We’ll show you more in lab 1

Aug 24, 2007 6

What is OOP?

Object-Oriented Programming (OOP) is a different way of thinking about a programming problem.

Rather than looking at a problem as some data and functions (procedures) that manipulate that data, we look at a problem and think about what “things” (objects) must be represented in the problem What are the attributes/properties/characteristics of each

object What are the behaviors of each object

Aug 24, 2007 7

More OOP

How is OOP different than programming in a language like C?

With C, your program consists of lots of functions being called from main, or calling each other. Functions are the focus.

With OOP (using Java/C++) your program consists of lots of objects used to represent “things” in your program. The objects use each other’s services.

Aug 24, 2007 8

What’s an Object? A bundle of related

data which make up the object’s “state” operations which define the objects “behavior”

Data are referred to as “instance variables” Operation are referred to as “methods”

Aug 24, 2007 9

Object Examples Bank Account

State: account number, owner’s name, balance, interest rate, etc

Operations: deposit, withdraw, transfer, etc Student

State: name, ID, birthday, major Operations: compute age, compute tuition, lookup grades

String State: sequence of characters Operations: compute length, test for equality, concatenate,

etc.

Aug 24, 2007 10

What is Java?

Created by Sun Microsystems team led by James Gosling (1991)

Originally designed for programming home appliances Difficult task because appliances are controlled by

a wide variety of computer processors Team developed a two-step translation process to

simplify the task of compiler writing for each class of appliances

Aug 24, 2007 11

Significance of Java translation process Writing a compiler (translation program) for each

type of appliance processor would have been very costly

Instead, developed intermediate language that is the same for all types of processors : Java byte-code

Therefore, only a small, easy to write program was needed to translate byte-code into the machine code for each processor

Aug 24, 2007 12

Why Java?

Popular Modern Language Used in many applications Desirable Features

Object-oriented Garbage Collection Portability of Byte Code Simpler GUI programming

Aug 24, 2007 13

Java is an Object-Oriented Language

Programming methodology that views a program as consisting of objects that interact with one another by means of actions (called methods)

Objects of the same kind are said to have the same type or be in the same class

Other high-level languages have constructs called procedures, methods, functions, and/or subprograms These types of constructs are called methods in Java All programming constructs in Java, including methods, are

part of a class

Aug 24, 2007 14

Java Applications

There are two types of Java programs: applications and applets

A Java application program or "regular" Java program is a class with a method named main When a Java application program is run, the run-

time system automatically invokes the method named main

All Java application programs start with the main method

Aug 24, 2007 15

Applets

A Java applet (little Java application) is a Java program that is meant to be run from a Web browser Can be run from a location on the Internet Can also be run with an applet viewer program for

debugging Applets always use a windowing interface

In contrast, application programs may use a windowing interface or console (i.e., text) I/O

Aug 24, 2007 16

Java Byte-Code The compilers for most programming languages

translate high-level programs directly into the machine language for a particular computer Since different computers have different machine

languages, a different compiler is needed for each one In contrast, the Java compiler translates Java

programs into byte-code, a machine language for a fictitious computer called the Java Virtual Machine (JVM) Once compiled to byte-code, a Java program can be used

on any computer, making it very portable

Aug 24, 2007 17

Java Virtual Machine

The JVM is the program that translates a program written in Java byte-code into the machine language for a particular computer when a Java program is executed The JVM translates and immediately executes

each byte-code instruction, one after another Translating byte-code into machine code is

relatively easy compared to the initial compilation step

Aug 24, 2007 18

Compiling and Running C/C++

C/C++ Code

Linux binary

Windowsbinary

Linux executable

Windowsexecutable

Project Library for Linux

Project Library for WindowsLinux C/C++ compiler

Windows C/C++

compiler

Linux C/C++ linker

Windows C/C++ linker

Aug 24, 2007 19

Compiling and Running Java

JavaCode

JavaBytecode

JRE for Linux

JRE for Windows

Java compiler

Hello.java

javac Hello.java

Hello.class

java Hello

java Hello

Java interpreter translates bytecode to machine code in JRE

Aug 24, 2007 20

Java Terminology

The Java acronyms are plentiful and confusing. Here are the basics.

JRE – Java Runtime Environment This is the Java Virtual Machine (JVM) that executes your Java

byte code JDK (formerly SDK) – Java Development Kit

JRE + tools (compiler, debugger) for developing Java applications and applets

J2SE – Java 2 Platform, Standard Edition The JRE and JDK products taken as a “family”

JSE API – application programming interface for the class libraries included with the JSE

To learn more about JDK, JRE, etc, visithttp://java.sun.com/javase/technologies/index.jsp

Aug 24, 2007 21

Java Versions

The current version of Java is Java 6, also known as Java 1.6 or Java 1.6.0 This is the version running on GL servers

The previous version was Java 5, also known as Java 1.5, Java 1.5.0 or “Java 2 SE Version 5” This is the recommended version for your PC/laptop

To learn find what version is on your PC/laptop, visit http://www.javatester.org/version.html

To learn more about Java version naming, visit http://java.sun.com/javase/namechange.html