Computer Science PRAXIS study guide

Software System Life Cycle

Analysis -> Design -> Implement(Code) -> Test -> Maintain -> Analysis -> ...

Top-Down Design (stepwise refinement)

break down into smaller and smaller pieces, easy to implement

Bottom Up Design

uses pre-existing modules/libraries, saves time and effort

Object oriented Programming (OOP)

interacting objects, data centered, bundles actions and processes with data, very large projects can be developed more easily, modifications can be made without altering the "insides"

3 Big Ideas of OOP

abstraction(encapsulation), inheritance, and polymorphism

Flowchart Shape: diamond

decision (boolean)

Flowchart Shape: rectangle

process

Flowchart Shape: paralellogram

input/output

Flowchart Shape: oval

start/end

Unified Modeling Language (UML)

visual organizer showing objects and contents

UML visual example

Name of class

------------------------

Attribute name: type

[set of variables, attributes, etc.]

-------------------------

Methods (parameters)

.

.

.

return type

Waterfall Development Model

linear progress, works in industry, not software, clear and straightforward but rigid and difficult to modify, changes are costly

idea -> analysis -> design -> develop -> test -> final

Incremental Development Design

small amount done at a time, test and adjust as needed, completes entire process in each increment, flexible to change, includes customer testing

plan -> analyze,design,implement(development) -> test -> evaluate -> plan -> ...

Spiral Development Design

includes risk analysis, documentation is difficult, uses prototyping and best parts of other models, costly and complex to manage

communicate -> plan -> model -> construct -> deploy -> communicate -> ...

Agile Development Design

commonly used in software development, can cause loss of focus or more complex project, risk of going over budget, incremental and iterative, flexible

sprint - set small simple short-term goals, achieve, test, evaluate, repeat

some common examples: SCRUM, XP, Kanban

code style conventions for constants

CAPS

code style conventions for class

Firstlettercapital

code style conventions for method/variable

CamelCase

Precondition

what must be true for the code to be executed

Postcondition

what will be true after the code is executed

Robust Program

able to withstand adverse conditions ("handle exceptions")

Unit Testing

process of testing each individual process

Input Protection/Data Validation

include a test of the form of input data

Exception

error in programming (checked or unchecked)

Exception Handling

protecting against exceptions

Try Catch Block

common exception handler

string

try {...}

catch {...}

Class vs. Object

definition of thing vs. actual thing

ex) recipe vs. meal

ex) blueprint vs. building

Encapsulation

object is defined as single entity with several inter-working parts

Abstraction(information hiding)

User is not privy to how inner parts work, but understands how to interface for use

ex) cars, computers, TV

Imperative(Procedural) Programming

code describes in exact detail what steps computer must make

Functional Programming

pure functional approach to problem solving

Inheritance

defining an object just like another but with more details, or extra details

[test "is a": one object "is a" form of another]

"Is a" Test

If one object "is a" form of another this is an example of inheritance

Parent Class

original class

Child Class

Inheriting class

Composition

made of predefined parts, several objects make one large object

[test "has a": a car "has a" body]

"Has a" Test

if an object "has a" different object this is an example of composition

Polymorphism

"many forms", redefining methods as needed

3 situations: overloading, overriding, polymorphic objects

Overloading

type of polymorphism, same name but operate different parameters to perform the same task

ex) car door lock is opened with a key or remotely

Overriding

type of polymorphism, redefining

Polymorphic Objects

type of polymorphism, parent can reference any child or grandchild

ex) furniture -> wooden furniture -> chair

a chair is still also furniture

Instruction Set Architecture (ISA)

part related to programming (native data types, instructions, external input/output, exception handling, registers, memory architecture)

Complex Instruction Set Computing (CISC)

micro-processor architecture, the machine instruction set designated as complex, primarily used by Intel and Intel Pentium; processors contain numerous instruction sets

Reduced Instruction Set Computing (RISC)

micro-processor architecture, few instructions, limiting to frequently used instructions, used by MacIntosh and Apple

Computer Architecture

relates to the way circuit boards and processors are designed and defined (CPU most significant)

Operating System (OS)

software that manages hardware and provides common services

Disk Operating System (DOS)

1966, first widely installed OS, operates using the command line, mainly IBM 1981-1995

Windows OS

1.0 released 11/20/1985,

XP - used underpinnings advanced security, stability, efficiency

vista - 2006, windows search, DVD maker, aimed to increase peer to peer file sharing

windows 8 - 2012, optimized for touch systems

Unix

family of multitasking, multiuser OS derived from AT&T, developed 1970s by Bell Labs, Ken Thompson, Dennis Ritchie

Linux

Linus Torvalds 10/5/1991, Unix-like open-source software, defining component was Linux kernel

Mac OS

1984, graphical user interface OS, Apple and MacIntosh

Mac OSX 2001

GM-NAA I/O

1956, forst OS for IBM 704 computer, General Motors, aeronautical research

Master Control Program (MCP)

1961, first OS with multiple processors, first commercial implementation of virtual memory, first OS written exclusively in a high level language

Artificial Intelligence

logic processes performed by software using sophisticated logic and large database systems

Low Level Language

easy for computer to understand and execute, written in machine code

High Level Language

easy for human to understand, must be translated into machine language to execute

Machine Code

original low level language, rows of switches flipped on or off by operator

Assembly

one step above machine, made easier to express programs, converts to machine code

Two Ways to Translate High Level Language to Machine Code

interpret

compile

Interpret

translated and executed line by line

Compile

translate all, then execute

Three Paradigms of High Level Language

procedural

functional

object oriented

Procedural (Structured Programming)(Imperative Languages)

first to develop, contain step-by-step instructions

ex) Fortran, Cobol, Pascal, C

Functional

"mathy", given data, recursion primary way to iterate process

ex) LISP, Haskell, Scheme

Object Oriented (OOP)

actions and data bundled in objects defined by classes

ex) C++, Java, Python

Fortran (Formula Translation)

1950s John Backus, used for science and engineering

COBOL

late 50s/early 60s Grace Hopper, used for business

BASIC (beginner's All-Purpose Symbolic Instruction Code)

1964 Dartmouth College, easy to learn and use, good for new or young programmers

Pascal

late 60s Niklaus Wirth, used as a teaching language

C and C++

1970s, replaces Pascal, general purpose, further developed OOP

Programming Language used on AP exams

1984 Pascal - 1sy Ap comp sci exam

1999 C++

2003 Java

Java

early 90s Sun Microsystems, James Gosling, used by engineers, popular present day, not compiled into machine but instead bytecode(portable code) which is then translated by each device and OS

Bytecode

universally portable software (Java uses)

ex) a game made for Xbox and Nintendo uses the same code but each console translates to what they need in order to execute

Python

Guido Van Rossum, named for Monty Python, supports procedural, functional, and OOP, general purpose high level language, emphasizes code readability

Visual Basic

1991 Microsoft, event-driven, easy to learn and used to create GUI based programs

XML (Extensible Markup Language)

set of rules defined for encoding documents in a format readable by both human and machine

Assembly Language

low level language using mnemonic opcodes (such as mov, sto, load) to directly interact with CPU, used by experts for highly efficient/fast programs

Backus Naur Notation

used to describe syntax in a context-free way

Pseudocode

informal high level description of algorithm, non-executable, meant to clearly express code

Syntax (Railroad Diagram)

graphical alternative to Bakus Naur

ex) if -> condition -> then -> statements -> else-if <(2 options) ...

float/double

data type, number with decimal values

int/short

data type, integer

char

data type, single entry text, 'enclosed in single quotes'

string

data type, multiple entry text, "enclosed in double quotes"

boolean

data type, true or false, 1 or 0

byte storage and limits

8 bits, values from -128 to 127

short storage and limits

16 bits, values from -32,768 to 32,767

int storage and limits

32 bits

long storage and limits

64 bits

char storage and limits

16 bits, cousin to int, number represents characters in ASCII/UniCode

ex) A=65, a=97, 0=48

Wraparound

reaching the end of an integer value and looping around to the other end

ex) byte num -> 127

num <- num + 1

print (num)

*output is -128 because byte max value is 127

float storage precision

32 bits, loses precision beyond 7 decimals

double storage precision

64 bits, loses precision beyond 15 decimals

Variable

location in memory containing a changeable value

Constant

memory location cannot be changed once assigned

Declare

assign name

Instantiated

assign a value to a declared variable

<- or = symbols used

a valid variable name... (5 identifier rules)

1. Must contain only letters, numbers, and underscore

2. Must begin with letter or underscore

3. May not contain symbols

4. May not contain spaces

5. May not be a reserved word from the language

coding conventions (6 rules of thumb)

1. classes start upper case

2. procedures, functions, and methods start lower case

3. camelCase multiple word identifiers

4. CONSTANTS are all caps

5. use meaningful names

6. abbreviate within reason

True or False: Assignment statements are "left to right" operation.

False, they are right to left operations, the right side compiles first, i.e. comp sci is not commutative

ex) num = 7 is good

ex) 7 = num is bad