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Overview of the Computer

• Definition: a programmable device that can store, retrieve, and process data.

• Hardware = physical components of a computer

• Software = computer programs (the set of all programs available on a computer). – application software and system software.

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Computer components:

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Programming Language

• Definition: languages with strict grammar rules, symbols, and special words used to construct a computer program

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Machine language

• the language that can be directly used and understood by the computer

• operations are very low-level, specific to the architecture (not portable)

• made up of binary-coded instructions (strings of 0s and 1s)

• exa: 110011 - add instruction

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Assembly Language

•A low-level programming language in which a mnemonic is used to represent each of the machine language instructions for a particular computer•Requires assembler

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COMP$PAY PROC PUBLIC;; COMP$PAY - procedure to compute gross pay ; (PAY = HOURS * RATE)MOV AX,HOURS ; multiplicandMUL RATE+2 ; X second word of multiplierMOV PAY+2,AX ; store the product in PAY;MOV AX,HOURS ; multiplicandMUL RATE ; times first word of multiplierADD PAY+2,AX ; add the product to PAYADD PAY,DX ; add the carry, if anyRET ; end procedure

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High-level languages

• Basic, C++, Pascal, Java, Ada, Modula-2, Cobol, Fortran…

• Similar to natural language (easier to use and debug)

• standardized description of the language exists

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High-level languages cont’d

• Not understood directly by a computer, must be converted to machine language: – Compilers: whole program is translated into

another language (machine language or bytecode) and then executed

– Interpreters: program is translated and executed one line at a time

• portable (machine-independent) – Program is written for any platform– compiler translates to each platform

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• C++ compiled to machine language– Requires translating to many different

machine languages

• Java compiled to Java bytecodes– One set of bytecodes can execute on many

different machines– intermediate level– machine language for theoretical computer:

Java Virtual Machine (JVM)

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Java

• Class– Unit of code that is the basic building block

of Java programs

• Java runtime– JRE– Executes compiled Java class files– Most computers have Java runtimes on

their computer

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Background

• Released by Sun in 1995

• Object-oriented

• Rich libraries – pre-written software

• Active programmer community

• API Specification– Application Programming Interface

• Extremely platform-independent

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Java Advantages

• Platform independence

• Reuse of code

• Security

• Automatic garbage collection

• Stronger typing of objects and variables

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Java Programming Environment

1. Type program as Java class =>.java2. Compile => .class (bytecode)3. Loader – connects bytecode from

various classes and loads bytecode into main memory

4. Interpreter – translate and run

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Sample program

public class Hello { public static void main(String[] args) { System.out.println("Hello World!“); }

}

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Java programs

• class Hello

• Class names begin with capital letter

• file Hello.java

• Class name and file name must match

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class• Unit of code that is the basic building block of

java programspublic class <name> //class header{ <method> <method> … <method>}main method is required public static void main(String[] args)

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methods• particular action or calculation

• main method is required

• Method header public static void main(String[] args)

{

statements

}

statements

• Command

• Statements end with ;

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System.out.println

• Line of output sent to console window• System.out.println("Hello World!");• System.out.println();• System.out.print("Hello");• //does not move to next line of output

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Literal string

• Surrounded by quotes• One line• Escape sequences

\t tab

\n new line

\” quotation

\\ backslash• System.out.println(" \"Slick\" Willy"); "Slick" Willy

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Example

System.out.println("This\nyields three lines\nof output\n");

This

yields three lines

of output

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Identifiers • used to name variables, constants,

methods, classes, and data types • Rules:

– must start with letter or underscore or $– Composed of letters, digits, $, or

underscore (better to start with a letter)

• Using Meaningful, Readable Identifiers!• Java is case sensitive• Don't use reserved words

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Identifiers

• Legal:

firstName

conversion

lengthOfRoom

payRate

counter1

x

• Illegal

first name

Hello!

5th

one+two

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Identifiers - Style Class name

Begin with capital letter Method

Begin with lowercase Exa: calcPay,getInfo, sum

• Constants: all caps• PI, MAX_HOURS, UNIV_NAME

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Comments• Compiler ignores comments

• /* */ everything between pair is ignored

• // - everything after the two slashes to the end of line is ignored

• header comment:• //Project number• //Student's name Date project is due• //Course number• //Purpose of the program

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When to use comments

• Comment variable and constant declarations.

• Precede blocks of code with an explanatory comment.

• Explain statements that are not obvious.• Precede each class with a brief header

comment

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Readability

• Class and method headers on lines by themselves

• One statement per line• Indent• Use whitespace liberally in the form of

blank lines and spaces.• Include at least one blank line between

methods

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Syntax

• Syntax - formal set of rules governing how valid instructions are written in a programming language

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Program Errors

• Syntax error – error in using Java, indicated by compiler– Cannot execute– Exa: File name does not match class name

• Logic error (bug) – code doesn't perform the intended task– debugging

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Structured Programming

• Control structures1. sequence

2. selection

3. Loop

• Modularity/Top-Down Design

– Decomposition – separation into parts

– Functions, procedures => methods

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Static method

• A block of statements that is given a name• Static

– allows non object-oriented invocation– Use no instance variable of any object they are

declared in

• Method call– Transfers control

• Methods can call other methods

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public class Memo { public static void main(String[] args) { printLogo(); //method call System.out.println("Reminder:" ); System.out.println("Company Meeting"); System.out.println("Thursday at 9:00!!!!"); printLogo(); } /* end main */ public static void printLogo() // method header { System.out.println("*************************************"); System.out.println("**********YOUR COMPANY********"); System.out.println("*************************************"); }}

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Design/Plan the solution

• Algorithm – a step by step procedure for solving a problem, ordered set of instructions such that:

• programs are implementations of algorithms, emphasis on writing algorithms.

• the computer is a fast and flexible tool for implementing algorithms.

• tools– flowcharts – Pseudocode– subtasks - hierarchy chart

• test solution for correctness - trace