1.3 Problem Solving The purpose of writing a program is to solve a problem The general steps in problem solving are: Understand the problem Dissect the problem into manageable pieces Design a solution Consider alternatives to the solution and refine it Implement the solution Test the solution and fix any problems that exist

1.3 Problem Solving Many software projects fail because the developer didn't really understand the problem to be solved We must avoid assumptions and clarify ambiguities As problems and their solutions become larger, we must organize our development into manageable pieces

1.3 Java A programming language specifies the words and symbols that we can use to write a program A programming language employs a set of rules that dictate how the words and symbols can be put together to form valid program statements The Java programming language was created by Sun Microsystems, Inc. It was introduced in 1995 and it's popularity has grown quickly since It is an object-oriented language

1.3 Java Program Structure In the Java programming language: A program is made up of one or more classes A class contains one or more methods A method contains program statements A Java application always contains a method called main See Lincoln.java (page 27)

1.3 Lincoln.java //******************************************************************** // Lincoln.java Author: Lewis/Loftus/Cocking // // Demonstrates the basic structure of a Java application. public class Lincoln { //----------------------------------------------------------------- // Prints a presidential quote. public static void main (String[] args) System.out.println ("A quote by Abraham Lincoln:"); System.out.println ("Whatever you are, be a good one."); }

1.3 Java Program Structure // comments about the class public class MyProgram { } class header class body Comments can be placed almost anywhere

1.3 Java Program Structure // comments about the class public class MyProgram { } // comments about the method public static void main (String[] args) { } method header method body

1.3 Comments Comments in a program are called inline documentation They should be included to explain the purpose of the program and describe processing steps They do not affect how a program works Java comments can take three forms: // this comment runs to the end of the line /* this comment runs to the terminating symbol, even across line breaks */ /** this is a javadoc comment */

1.3 Identifiers Identifiers are the words a programmer uses in a program An identifier can be made up of letters, digits, the underscore character ( _ ), and the dollar sign Identifiers cannot begin with a digit Java is case sensitive - Total, total, and TOTAL are different identifiers By convention, Java programmers use different case styles for different types of identifiers, such as title case for class names - Lincoln upper case for constants - MAXIMUM

1.3 Reserved Words Special identifiers called reserved words already have a predefined meaning in the language A reserved word cannot be used in any other way The Java reserved words: (page 31) abstract boolean break byte case catch char class const continue default do double else extends false final finally float for goto if implements import instanceof int interface long native new null package private protected public return short static strictfp super switch synchronized this throw throws transient true try void volatile while

1.3 White Space Spaces, blank lines, and tabs are called white space White space is used to separate words and symbols in a program Extra white space is ignored A valid Java program can be formatted in many ways, but should be formatted to enhance readability, using consistent indentation See Lincoln2.java (page 33) See Lincoln3.java (page 34)

1.3 Lincoln2.java //******************************************************************** // Lincoln2.java Author: Lewis/Loftus/Cocking // // Demonstrates a poorly formatted, though valid, program. public class Lincoln2{public static void main(String[]args){ System.out.println("A quote by Abraham Lincoln:"); System.out.println("Whatever you are, be a good one.");}}

1.3 Lincoln3.java Lincoln3 { public static void main ( String [] //******************************************************************** // Lincoln3.java Author: Lewis/Loftus/Cocking // // Demonstrates another valid program that is poorly formatted. public class Lincoln3 { public static void main ( String [] args ) System.out.println ( "A quote by Abraham Lincoln:" ) ; System.out.println "Whatever you are, be a good one." ) ; }

Homework: Read Section 1.3 Multiple Choice # 1.6 – 1.8 True/False # 1.1, 1.5, 1.7 Short Answer # 1.7 & 1.8

Writing your first program: Log onto your computer Make a new folder in your h:\drive: MyJavaWork Open Jcreator (find in Math Shortcuts under Start menu) File  New  Blank Workspace

Click on Finish

Setting up your projects: File  Open Workspace

Workspace Opened:

Make a new project: File  New  Project Empty Project  Next

Name each project: First Program  Finish  Finish

Name your file Put your curser on your project name: First Program File  New  File  Empty Java File  Next

Entering the file name Type the name of your file: HelloWorld You do not need to type in the .java extension – it is automatic Click on Finish

Write your first program

Build your Project Build  Build Project

Run Your Project Once your output at the bottom of the screen says “process completed” then choose” Run  Run Project If you do not see “process completed” you will see error messages. You must fix your errors and build again before running the project.

Program with output at bottom:

Your Turn: Click on Workspace Chapter 1 Programs Go to File  New  Project  Empty Project Name your next project Second Program Be sure your file path is directed to your h:\drive and the MyJavaWork folder Once you have a new project, click on the project name Go to File  New  File  Empty Java File Name this file Greeting Click on Finish Type the code for a new program that will print some sort of greeting to the screen instead of “Hello World!”

Use the following as a start: Add your own comments

1.4 Language Levels There are four programming language levels: machine language assembly language high-level language fourth-generation language Each type of CPU has its own specific machine language The other levels were created to make it easier for people to read and write programs

1.4 Programming Languages A program must be translated into machine language before it can be executed on a particular type of CPU A compiler is a software tool which translates source code into machine language

1.4 Java Translation Another software tool, called an interpreter, translates bytecode into machine language and executes it in short bursts Java is considered to be architecture-neutral – will work on many different machines.

1.4 Java Translation Java source code Java bytecode Java compiler Java interpreter Bytecode compiler Machine code

1.4 Development Environments There are many environments for developing Java software: Sun Java Development Kit (JDK) Sun Forte for Java Borland JBuilder MetroWerks CodeWarrior Microsoft Visual J++ Eclipse BlueJ ** JCreator LE

1.4 Syntax and Semantics The syntax rules of a language define how we can put together symbols, reserved words, and identifiers to make a valid program The semantics of a program statement define what that statement means (its purpose or role in a program) A program that has correct syntax is not necessarily logically correct A program will always do what we tell it to do, not what we meant to tell it to do

1.4 Errors A program can have three types of errors The compiler will find syntax errors or compile-time erros and other basic problems, which cause the program not to execute A run-time error can occur during program execution, which causes a program to terminate abnormally, such as trying to divide by zero A logical error occurs when the program executes, but produce incorrect results, perhaps using an incorrect formula

1.4 Errors Debugging – finding and correcting defects in a program Why is it called debugging?

Homework: Read pp. 33 – 41 Short Answer p 52 # 1.9

1.5 Introduction to Graphics A picture or drawing must be digitized for storage on a computer A picture consists of pixels, and each pixel is stored separately

1.5 Representing Color A black and white picture can be stored using one bit per pixel (0 = white and 1 = black) A colored picture requires more information; there are several techniques for representing colors For example, every color can be represented as a mixture of the three additive primary colors Red, Green, and Blue In Java, each color is represented by three numbers between 0 and 255 that collectively are called an RGB value

1.5 Coordinate Systems Each pixel can be identified using a two-dimensional coordinate system When referring to a pixel in a Java program, we use a coordinate system with the origin in the top-left corner Y X (0, 0) 112 40 (112, 40)

Programming Assignment Do programming exercises from the text pp 52 - 53: 1.1, 1.3 – 1.6 Read pp. 42 – 44.