©2004 brooks/cole chapter 1: getting started sections covered: 1.1introduction to programming...

©2004 Brooks/Cole

Chapter 1: Getting Started

Sections Covered:1.1 Introduction to Programming1.2 Constructing a Java Program1.3 The print() and println() Methods1.4 Programming Style1.5 Creating a Dialog Box

Figures ©2004 Brooks/ColeCS 119: Intro to Java Fall 2005

Programming

• Computer hardware by itself doesn't do anything

• Software in the form of a program tells the computer what to do– Low-level programs are written in the

processor's language of 0s and 1s– High-level programming languages are easier

for people to understand


Programs process data

A typical program does three things1. Get some input data2. Transform the input data to produce a result3. Output the result


The Two Distinct Java Environments


Sample java Programs

• DisplayHelloWorld.java– A console application

• HelloDisplay.java– Graphical (windowed) applications

• HelloApplet.java– An Applet is a program that is run by a web

browser


Algorithms

• Before you can tell the computer what to do, you have to figure out how to do what needs to be done.

• An algorithm is a step-by-step procedure describing what needs to be done.

• Two ways to describe an algorithm– Pseudocode - use words to describe the process– Flowcharts


Algorithms for

Summing the Numbers from1 through 100


•Flowchart Symbols


Flowchart for Calculating the Average

of Three Numbers


A Simple Paint-by-Number Figure


Coding an Algorithm

Once you have a correct algorithm, writing the program is easy.


Object-Oriented Programming

• Java is an object-oriented language

• In object-oriented programs we use classes and objects to help organize our program

• Objects have– Data– Behavior

• A class defines what the data and behavior should be for a particular kind of object


Using UML Diagrams

• Pictures can be easier to understand than large amounts of text

• UML is a diagram language for describing object-oriented programs

• There are many different kinds of diagrams– We'll use only a few of them


The Rectangle Class

• Suppose we have a class to represent a rectangle.– The properties of a rectangle

are the length and width– From these we can determine

the area or the perimeter– We should be able to change

the properties– We might want to dispplay the

properties


A Set of Rectangle Objects

Once the Rectangle class is defined, you can create rectangle objects

Each Rectangle has its own value of length and width


Sending a Message to a Rectangle Object

We can send a message to a Rectangle object

In this case, the object replies to our message by sending back the area


The Traditional Translation Process

From code to executable

•Program code is written in a high-level language•A processor understands binary code (0s and 1s)•A program needs to be translated from high-level code to the low-level code that the computer understands


Compiling and Executing a Java

Program

Java works a little differently1. Convert high-level code to byte-code2. Use another program to execute the

byte-code

Under Linux1. javac converts source code into byte

code• Result has extension .class

2. java executes the byte-code file


Constructing a Java Program

• Every Java program consists of one or more classes

• One class must be a main class– The main class must contain a method called

main


A Simple Java Program


Class Header

public class Hello

• public - modifier specifying visibility of the class

• class - keyword that is part of the Java syntax for creating a class

• Hello - an identifier used to name the class


Method Header

public static void main( String[] args)

• public - modifier specifying visibility of the method

• static - modifier specifying class method• void - keyword specifying no return value• main - an identifier used to name the method• (String[] args) - parameter list


A Well-Designed ProgramIs Built Using Modules


Modules

• We use classes to construct modules in Java

• Within a class, methods can be used to modularize functionality– If you have some operation that is done in

several different places, make a method


Keywords and Identifiers

• Keywords are words that have special meaning in the java language– Keywords are reserved; they can't be used as names

– Keywords need to appear in the correct context

• Identifiers are used for naming things– Objects, classes, methods all need names

– Rules for naming• First character must be letter or underscore (_)

• Remaining characters can be letters, digits or underscore


Syntax

• Syntax is the rules that specify how the words in your program can be arranged.

• Programming language syntax is simpler that natural language syntax.– Because it has to be translated by a program -

programs are less flexible than people


Output to the Console

• Most of our programs will be console applications– Output appears on the console

• The System class has an object called out that you use to send output to the console– out is a PrintStream object

– PrintStream has two methods that send text to the console

• print( text)

• println( text)


print and println

• Text output with print starts at the current cursor position and continues until the text ends

• Text output with println start starts at the current cursor position and continues until the text ends and then appends a newline– Next output will appear at the beginning of the

next line.


Escape sequences

• What if you need to make a single String extend over more than one line?– Text enclosed in double quotes needs to fit on a single

line in your program. Typing return breaks it onto two lines.

• The backslash (\) character is used for representing characters that you can't just type.– \n is the newline character– \" allows you to put double quotes in a double-quoted

string– \\ allows you to put a backslash in your string


Programming Style

• The java compiler doesn't care how many lines you use for your program statements

• The people who have to read your code will find it easier if you format it nicely.

• Look at the examples in the book for one common formatting style

• Sun has a recommended style for Java programs


Comments

• We often need to put text into a program to help explain the code

– We call this kind of text comments– We want the compiler to ignore comments

• Java has three types of comment1. // starts a one-line comment2. /* … */ encloses multiline comments3. /** … */ encloses javadoc comments


Dialog Boxes

• The JOptionPane class has several class methods for creating common dialog boxes.

• showMessageDialog is used for providing information to the user of a GUI program

• Creating GUI programs entirely out of dialog boxes is rather tedious for the user.


showMessageDialog() Dialog Boxes

WARNING_MESSAGE QUESTION_MESSAGE

PLAIN_MESSAGE

ERROR_MESSAGEINFORMATION_MESSAGE


The Dialog Produced by MultiLineDialog.java

©2004 brooks/cole chapter 1: getting started sections covered: 1.1introduction to programming...

Documents

brookscole cs

result slide

width slide

brookscole chapter

number figure slide

dialog box slide

web browser slide

rectangle class