Chapter 1: Computer Systems

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Kursusform 

• 13 uger med:
• Undervisning i klassen 1,5-2 timer
• Opgave ”regning” i databar (løsninger på hjemmeside)
• En midtvejsopgave der afleveres og rettes
• 2 uger med:
• Praktisk opgave i grupper med rapport
• 1 uge med:
• Mundtlig eksamen (rapport+teori)

• Lærere: 
  
• Ole Remmer
• Mads Nyborg
• OBS – Dette er et universitet – sørg selv for at læse!

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Vigtige links 

• www.campusnet.dtu.dk
• www.imm.dtu.dk/courses/02312
• java.sun.com/j2se
• www.eclipse.org

Chapter 1:  Computer Systems 

Presentation slides for 

Java Software Solutions

Foundations of Program Design

Third Edition 

by John Lewis and William Loftus 

Java Software Solutions is published by Addison-Wesley 

Presentation slides are copyright 2002 by John Lewis and William Loftus. All rights reserved.

Instructors using the textbook may use and modify these slides for pedagogical purposes.

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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. (new C# from MS much the same)
• It was introduced in 1995 and it's popularity has grown quickly since
• It is an object-oriented language

 

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Java Program Structure 

• In the Java programming language:
• A program (application) is made up of one or more classes
• A class contains one or more methods
• A method contains program statements
• These terms will be explored in detail throughout the course
• A Java application always contains a method called main

 
 

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Java Program Structure 

public class MyProgram 

{ 
 
 
 
 
 
 
 
 

} 

//  comments about the class 

class header 

class body 

Comments can be placed almost anywhere

 
 

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Java Program Structure 

public class MyProgram 

{ 
 
 
 
 
 
 
 
 

} 

public static void main (String[] args) 

{ 
 

} 

//  comments about the class 

//  comments about the method 

method header 

method body

 
 

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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   */

 
 

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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

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Identifiers 

• Sometimes we choose identifiers ourselves when writing a program (such as Lincoln)
• Sometimes we are using another programmer's code, so we use the identifiers that they chose (such as println)
• Often we use special identifiers called reserved words that already have a predefined meaning in the language
• A reserved word cannot be used in any other way

 
 

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Reserved Words 

• The Java reserved words:

 

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

 

 
 

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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
• Programs should be formatted to enhance readability, using consistent indentation
• See Lincoln2.java (page 37)
• See Lincoln3.java (page 38)

 

 
 

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Programming Languages 

• A program must be translated into machine language before it can be executed on a particular type of CPU
• This can be accomplished in several ways
• A compiler is a software tool which translates source code into a specific target language
• Often, that target language is the machine language for a particular CPU type
• The Java approach is somewhat different

 
 

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Java Translation 

• The Java compiler translates Java source code into a special representation called bytecode
• Java bytecode is not the machine language for any traditional CPU
• Another software tool, called an interpreter, translates bytecode into machine language and executes it
• Therefore the Java compiler is not tied to any particular machine
• Java is considered to be architecture-neutral

 
 

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Java Translation 

Java source

code 

Machine

code 

Java

bytecode 

Java

interpreter 

Bytecode

compiler 

Java

compiler

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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++
• Symantec Café
• Monash BlueJ
• JCreator
• Though the details of these environments differ, the basic compilation and execution process is essentially the same (often using the JDK)

 
 

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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 is syntactically correct is not necessarily logically (semantically) correct
• A program will always do what we tell it to do, not what we meant to tell it to do

 
 

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Errors 

• A program can have three types of errors
• The compiler will find syntax errors and other basic problems (compile-time errors)
• If compile-time errors exist, an executable version of the program is not created
• A problem can occur during program execution, such as trying to divide by zero, which causes a program to terminate abnormally (run-time errors)
• A program may run, but produce incorrect results, perhaps using an incorrect formula (logical errors)

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Basic Program Development 

errors 

errors 

Edit and

save program 

Compile program 

Execute program and

evaluate results