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Chapter 1 - Introduction. 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 environment and your compiler

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ch 1goals
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
1 1 what is programming
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?
1 2 anatomy of a computer
1.2 Anatomy of a Computer
  • A computer is a machine that can do certain tasks
    • Stores data
    • Interacts with devices
    • Executes programs
slide5
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
1 2 anatomy of a computer1
1.2 Anatomy of a Computer
  • Storage – where data is kept
    • 3 types – primary, secondary, removable
1 2 anatomy of a computer2
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
slide9
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?
1 3 translating human readable programs to machine code
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
machine code
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
what s the problem
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
assembly
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.
high level
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
1 4 the java programming language
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
java virtual machine
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.
flaws
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
1 5 becoming familiar w your computer
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
1 6 compiling a simple program
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.
simple program
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!”);

}

}

essential components
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
method
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
parameters
Parameters

public static void main(String[] args)

  • String[] args is a parameter – input given to a method (will learn about more later on)
slide24
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 ;
comments
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

*/

method call
Method Call
  • Here, we are calling the method println() on the object System.out
notes
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!
1 7 errors
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
1 8 compilation process
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
coding loop
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
object oriented programming
Object Oriented Programming
  • What is the point of this course?
    • Not Java – its just a tool
    • Methodology of programming – OOP
objects classes 2 main concepts
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.
classes
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
messages and methods
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