Chapter 1 - Introduction

1. Chapter 1 - Introduction

2. Ch 1Goals • To understand the activity of programming • To learn about the architecture of computers • To learn about machine code and high level programming languages • To become familiar with your computing environmentand yourcompiler • To compile and run your first Java program • To recognize syntax and logic errors

3. 1.1 What is Programming? • Computers are programmed to perform tasks • Different tasks = different programs • Program • Sequence of basic operations executed in succession • Contains instruction sequences for all tasks it can execute • How do we produce this program?

4. 1.2 Anatomy of a Computer • A computer is a machine that can do certain tasks • Stores data • Interacts with devices • Executes programs

5. CPU • Central Processing Unit (CPU) - Heart of the computer • Made of a chip (AMD, Intel, etc), millions of transistors • Executes instructions given by a program

6. 1.2 Anatomy of a Computer • Storage – where data is kept • 3 types – primary, secondary, removable

7. 1.2 Anatomy of a Computer • Computers communicate through a network • Peripheral devices allow interaction with humans • Speakers, screen, printer, scanner • RAM, Disks, peripherals connected to CPU via the bus

9. Where is a program stored when it is not currently running? • Which part of the computer carries out arithmetic operations, such as addition and multiplication?

10. 1.3 Translating Human-Readable Programs to Machine Code • There are actually multiple levels upon which a program can be written • Machine Instructions • Assembly • High Level Language

11. Machine Code • The most basic level of instructions • Everything is represented with numbers (read in binary) • Looks like this: 00010101 00101000 (binary) 21 40 (decimal) • This is the only language the CPU knows

12. What’s the problem? • CPUs perform very primitive operations only • Add, subtract, load from memory • Leads to coding of several hundred lines to perform one simple operation • Not Intuitive • Can you look at 1000 numbers and tell what the program is doing? • Each CPU uses a different set of instructions • Each CPU translates different digits to mean different things

13. Assembly • A slight step up from machine • Uses words and numbers • load 40 • Still needs as many instructions as machine language, but is slightly easier to read.

14. High Level • High level is much more expressive • One statement is converted into several machine code instructions • The conversion is done by the compiler • Very complicated and sophisticated, not the focus of this course

15. 1.4 The Java Programming Language • Simple • Safe – more secure, easier to catch errors • Platform-independent ("write once, run anywhere") – operating system and architecture • Rich library (packages) • Designed for the Internet

16. Java Virtual Machine • Unique to Java • Instead of compiling for a particular processor, Java compiles to a virtual processor that is the same for every computer • Lesson: The code is the same no matter what computer you are on, so you don’t have to make a Mac version and a PC version, etc.

17. Flaws • Fully object-oriented nature can be confusing to beginning programmers • Many revisions made – make sure you update if you work from home to Java 5.0 (1.5) • Rich libraries  So much to learn

18. 1.5 Becoming Familiar w/ your Computer • Very important to familiarize yourself with your computer • Understand how to find files, what they are, how do you move them around and name them • Understand files and folders • Programs are kept in files • File: a collection of items of information that are kept together • Files have names, and the rules for legal names differ • Files are stored in folders or directories

19. 1.6 Compiling a Simple Program • So how do we actually make a program? • In this course, we will use an IDE (Integrated Development Environment) called Eclipse • This will help us find mistakes more quickly.

20. Simple Program • Most simple program • Outputs a sentence to the console screen public class FirstProgram { public static void main(String[] args) { //display a greeting in the console window System.out.println(“My First Program!”); } }

21. Essential Components • What does each line mean? public class ClassName • A class is an essential part of a java program, all instructions are contained within a class • We create a class called FirstProgram, the file must be called FirstProgram.java

22. Method public static void main(String[] args) { // Code goes here } • Classes contains methods – specific instructions that can be called • Ex. Robot needs method called walk public void walk() { } • Every program must have a method called main – it is the method called first

23. Parameters public static void main(String[] args) • String[] args is a parameter – input given to a method (will learn about more later on)

24. Body • The instructions are the body of a method System.out.println(“My First Program!”); • An instruction to print a message to the screen • Each instruction ends in a ;

25. Comments //display a greeting in the console window System.out.println(“My First Program!”); • “//” signifies not to execute this line of code • Has many uses – here it is to explain what the code is supposed to do • Another type of comments: /* Multiple lines of comments about what is going on */

26. Method Call • Here, we are calling the method println() on the object System.out

27. Notes • Java is case sensitive class FirstProgram ≠ class firstprogram • It is free form – the amount of white space is irrelevant to the computer (although it is important for readability) • You could have all instructions on one line, but not very useful to a human • We will grade on it!

28. 1.7 Errors • Two types of errors • Compile Time Errors – Syntax errors • These are caught when you ask Java to convert your program to machine code • Your program must follow a set of rules (just like a sentence in English) • Run Time Errors • Not problems in the syntax, but problems in logic • Program does not accomplish what the programmer intended

29. 1.8 Compilation Process • The code a programmer creates is called the source code • Written in Java • Saved as a .java file • Must have the same name as the class • When converted by the compiler, a class file is created • Machine instructions • Saved by compiler as .class file

31. Coding loop • Edit-compile-test loop • Your programming begins with editing a file by writing instructions • When done, compile the program. • If no compile errors, test the program. If compile errors, go back to editing • If there are runtime errors, go back to fix them

32. Object Oriented Programming • What is the point of this course? • Not Java – its just a tool • Methodology of programming – OOP

33. Objects & Classes – 2 Main Concepts • Object – an entity, something we can imagine (typically a noun) • Consists of data values and operations for manipulating those values • Interactions between objects is the heart of OO style • Ex. Bank accounts – need Customer, Account, Bank, etc.

34. Classes • Class – Instructions for creating objects • Defines what objects can and cannot do – how they behave and what info they hold • Like a mold, template, or blueprint • Objects are instances of classes • Ex. Class is Student, instance is Eric Lantz • Ex2. Class is University, instances could be University of Wisconsin and Cornell

35. Messages and Methods • In order to use objects and classes, coder needs to communicate with them - Messages • Ex. Tell Robot to move forward 1 foot • Can you send any message to any object? • No, the object must understand the message • The class defines the messages that the object can understand