Chapter 1

1. Chapter 1 CSIS-120: Java Intro

2. What is Programming? • A: It is what makes computer so useful. • The flexibility of a computer is amazing • Write a term paper (Word processing program) • Balance checkbook (Accounting program) • Play a game (Games are programs) • Post on Facebook (Facebook is program) • Programming  Computer Programs

3. What is a Computer Scientist? • Somebody who can write programs to solve lots of different problems. • You don’t need to program to use programs • But, often times you need to program to solve an array of different problems.

4. Computer Hardware • Hasn’t changed as much as you would think. • See Diagram on page 6 • Programming has improved just as much as the hardware.

6. Evolution of programming • Early 60’s • Specify instructions in binary • 01010101101010101 • Late 60’s to 70’s • Machine language • Instruction codes and value in hexidecimal • 2F 4A0 • 56 C13

7. Evolution of programming • 70’s to Today • Assembly language (more general, more human readable – get translated into machine language) • SET r1, 10 ; r1 will take the place of i SET r2, 1 ; r2 will hold the value to subtract each timeLOOP1TOP:SUB r1, r1, r2 ; subtract one from r1 CMP r1, r0 JMP NEQ, LOOP1TOP ; • Late 70’s to Today • High level language • Designed for humans to “easily” read/write • C++, Java, etc.

8. Evolution of programming • 90’s to Today • Graphical languages • makes it even “easier” to program • Alice, Labview, etc. • But in the end it all get compiled to binary • High Level Language  Assembly Code  Machine Instructions  Binary

9. Compilation • High-level languages are compiled into machine language. • A compiler itself is a program that simply translates from high-level lanaguage to low-level. • Most compilers create machine language for a specific type of operating system/computer (called a platform) • PC Platform • Mac Platform • Unix Platform

10. Compilation & Java • A Java compiler creates “machine language” (Java Byte Code) that can be run on any type of computer. • The computer just needs a Java Virtual Machine (JVM) • The JVM is just a program that can execute Java Byte code for a specific computer. • In theory, your compiled program can run on any computer.

11. Traditional Compilation (C++) • The compiler eventually creates machine language for a specific operating system/computer platform (Windows, Mac, Linux, etc.) • If you wish to run you program on a PC and a Mac, you need two compilers and need to compile two different running programs. • In contrast, a Java program just needs to be compiled once. • But, the PC and Mac will both need installed JVMs (Java Virtual Machines)

14. Java is still very popular • Platform independence: Compiled programs can run on any device with a JVM installed. • Java Enterprise Edition EE • Java works well with the Internet & WWW • Rather than run programs on your computer, Java allows you to easily create programs that can run on a web server. • Java Server Pages (JSP) can “call” Java programs. • Thus, complex programs can be run from web-enabled devices (iPhone, Droid Phone, etc.) without actually “executing” the program locally • programs execute on the server.

15. Let’s start with a most basic program • Traditionally, the ‘hello world’ program is the first one taught in most classes/texts.

16. HelloPrinter.java 1 publicclass HelloPrinter 2 { 3 publicstaticvoid main(String[] args) 4 { 5 // Display a greeting in the console window 6 7 System.out.println("Hello, World!"); 8 } 9 } • Program Run: • Hello, World!

17. The Structure of a Simple Program: Class Declaration • Classes are the fundamental building blocks of Java programs: • public class HelloPrinter • starts a new class • A class defines a “reusable” programming object. • In a computer game, the classes might include things like • public class Zombie • public class RocketLauncher

18. Each class goes in a .java file • Every source file can contain at most one public class • The name of the public class must match the name of the file containing the class: • Class HelloPrinter must be contained in a file named HelloPrinter.java

19. The Structure of a Simple Program: main Method • Every Java application contains a class with a main method • When the application starts, the instructions in the main method are executed • publicstaticvoidmain(String[] args) • { • . . . • } • declares a main method

20. The Structure of a Simple Program: Comments • The first line inside the main method is a comment: • // Display a greeting in the console window • Compiler ignores any text enclosed between // and end of the line • Use comments to help human readers understand your program

21. The Structure of a Simple Program: Statements • The body of the main method contains statements inside the curly brackets ({}) • Each statement ends in a semicolon (;) • Statements are executed one by one • Our method has a single statement: • System.out.println("Hello, World!"); • which prints a line of text: • Hello, World

22. The Structure of a Simple Program: Method Call • System.out.println("Hello, World!"); • isa methodcall • A method call requires: • The object that you want to use (in this case, System.out) • The name of the method you want to use (in this case, println) • Parameters enclosed in parentheses (()) containing any other information the method needs (in this case, "Hello, World!")

23. Syntax1.1 Method Call

24. The Structure of a Simple Program: Strings • String: a sequence of characters enclosed in double quotation marks: • "Hello, World!"

25. SelfCheck1.10 • How would you modify the HelloPrinterprogram to print the words "Hello," and "World!" on two lines? • Answer: • System.out.println("Hello,"); System.out.println("World!");

26. SelfCheck1.12 What does the following set of statements print? System.out.print("My lucky number is"); System.out.println(3 + 4 + 5);

27. Editing a Java Program • Use an editor to enter and modify the program text • Java is case-sensitive • Be careful to distinguish between upper- and lowercase letters • Lay out your programs so that they are easy to read

28. Compiling and Running a Java Program • The Java compiler translates source code into class files that contain instructions for the Java virtual machine • A class file has extension .class • The compiler does not produce a class file if it has found errors in your program • The Java virtual machine loads instructions from the program's class file, starts the program, and loads the necessary library files as they are required

29. HelloPrinter in a Console Window

30. HelloPrinter in an IDE

31. FromSourceCodetoRunningProgram

32. Self Check 1.14 What do you expect to see when you load a class file into your text editor?

33. Errors • Compile-time error: A violation of the programming language rules that is detected by the compiler • Example: • System.ou.println("Hello, World!); • Syntax error • Run-time error: Causes the program to take an action that the programmer did not intend • Examples: • System.out.println("Hello, Word!"); System.out.println(1/0); • Logic error

34. Algorithms • Algorithm: A sequence of steps that is: • unambiguous • executable • terminating • Algorithm for deciding which car to buy, based on total costs: • For each car, compute the total cost as follows: • annual fuel consumed = annual miles driven / fuel efficiency • annual fuel cost = price per gallon x annual fuel consumed • operating cost = 10 x annual fuel cost • total cost = purchase price + operating cost • If total cost1 < total cost2 • Choose car1 • Else • Choose car2

35. Pseudocode • Pseudocode: An informal description of an algorithm: • Describe how a value is set or changed: • total cost = purchase price + operating cost • Describe decisions and repetitions: • For each car • operating cost = 10 x annual fuel cost • total cost = purchase price + operating cost • Use indentation to indicate which statements should be selected or repeated • Indicate results: • Choose car1

36. Program Development Process