ComSci Final

CPU

• central processing unit

• process a programs instructions

• cam only process very simple instructions

Main Memory

• working memory used to store current program, data the program is using, results of intermediate calulations

• RAM (random access memory)

Auxiliary Memory

• aka secondary memory

• HHD, SSD, CD, DVD, Blu-Ray, USB

• nonvolatile memory

Program

• a finite sequence of instructions for a computer to follow written in a programming language

Operating System

• OS

• a supervisory program that oversees the operation of the computer

• the main job of an OS is to manage process and hardware resources

  • eg retrieving and starting a program for you and manages resources like memory

Windows Commands

• interact with the Windows OS via Command Prompt

• Commons commands: dir, cd, cls, mkdir, tree, exit

Compile a Java File

javac MyProgram.java

Run a Java File

java MyProgram

Compiler

• translates a program from a high level langauge to a low level language the computer can run

• you enter source code into a compiler

• compilers produce machine or assembly language programs called object programs

• most high level languages need a different compiler for each type of computer and operating system

• translates the entire source code into machine code before execution

Java Byte Code

• the java compiler doesn’t translate a Java program into assembly language or machine language for a particular computer

• instead, it translates a Java prpgram into byte-code

• byte-code is the machine language for a hypothetical computer (or interpreter) called the Java Virtual Machine

• a byte-code program is easy to translate into machine language for any particular computer

• after compile a Java program into byte-code, tat byte-code can be used on any computer with a byte-code interpreter and without a need to recompile

Interpreter

• translates source code into machine code line by line during runtime

Package

• a library of classes that have been defined already

IDE

• intregrated development environment

• combines a text editor with commands for compiling and running Java programs

• 3 features of eclipse: tells you where errors are, control f (find), convenient project management

Object-oriented programming (OOP)

• our world consists of objects (people, trees, cars, etc)

• objects can perform actions which affect themselves and other objects in the world

• Object-oriented programming (OOP) treats a program as a colleciton of objects that intereact by means of actions

• objects are called objects

• actions are called methods

• objects of the same kind have the same type and are objects of the same class

• objects of the same class have a common set of methods and same the kinds of data but each object can have its own data values

• classes reflect concepts, objects refelct instances that embody those concepts

Algorithm

• finite sequence of instructions for solving a problem or performing some task

Types of Errors

• syntax error

• runtime error

• logic error

Syntax Errors

• grammatical mistakes in a program

• ex. not ending a statement with a semicolon

Runtime Errors

• errors that are detected when your program is running, but not during compilation

• ex. attempting to divide by 0

Logic/Semantic Errors

• errors that are not detected during compilation or while running, but which cause the program to produce incorrect results

Variables

• stores data

• value can be changed

  int styleChoice, numberOfChecks

  double balance, interestRate

  char jointOrIndividual

Data Types

• Primitive Type

  • byte, short, int, long, float, double, char, boolean

• Class/Object Type

  • String

Java Identifier

• an identifer is a name, such as the name of variable

• indentifiers may contain only: letters digits 0-9, the underscore character, the dollar sign symbol (we don’t use in the class)

• first character cannot be a digit

• can’t contain spaces, dots, astericks, or other characters

if-else statement

Tautology

• a boolean expression is a tautology if and only if it is always true regardless of the values of its variables

Contradiction

• a boolean expression is a contradiction if and only if it is always false regardless of the values of its variables

Contingency

• a boolean expression that is neither a tautology nor a contradiction is called contingency

==

• use for determining if two ints (or any primitive integer types), booleans, or chars have the same value

• don’t use for floating points

• don’t use for objects

compareTo()

• returns 0 if both are equal

• returns -1 if the first is lexigraphically greater than the second

• returns 1 if the first is lexigraphically lesser than the second

Ternary Operator/Conditional Operator

• useful with print and println statements

A program can be terminated normally by

System.exit(0);

Enumerations

• consider a need to restrict contents of a variable to certain values

• an enumeration lists the values a variable can have

The while Statement

The do-while Statement

The for Statement

The for-each Statement

Sentinel Value

• for large input lists, a sentinel value can be used to signal the end of the list

• ex. a negative number following a long list of nonnegative exam scores

The break Statement

• can be used to end a loop immediately

• the break statement end only the innermost loop or switch statement that contains the break statement

• we will not be using break statements in loops in this class

The continue Statement

• ends current loop iteration

• begins the next one

• we will not be using continue statements in loops in this class

Data Structures

• a particular way of storing and organizing data in a computer so it can be used effectively

• ex. array

Arrays

• an array is a special kind of Java object

• It is a collection of variables of the same type

• fized size

  double[] temperature = new double [7];

new Operator

• the new operator allocates memory for an object like an array on the program’s heap (as opposed the program’s stack)

Creating Arrays

type[] name;

name = new type[]{value1, value2, value3, …};

type[] name = {value1, value2, value3, …};

type[] name = new type[num];

Class definition

Constructor

• a constructor is a special method that intilizes objects of a class

• it shares the same name as the class and lacks a return type

Instance Variable

a variable declared within class, but outside of any specific method or constructor

static

• signifies that a variable or method is associated with the class itself, rather than with any specific instance

• static variables are shared by all objects of a class

• static variables are also called class variables

• static varaibles belong to the class not to an individual object

• a single copy shared by all instances of the class

final

ensures variables cannot be changed

methods cannot be overridden by subclasses

classes cannot be subclassed

The Keyword this

• inside the class the unnamed object can be referred to with the name this

• the keyword this stands for the current instance of the object

• it can be used to call methods or access instance variables in this object

Information Hiding

• programmer using a class method need not know details of implementation

• designing a method so it can be used without knowing details

• also refered to as abstraction

Pre- and Postcondition Comments

Precondition Comment:

• states condtion that must be true before method is invoked

Postcondition Comment:

• tells what will be true after method execution

public and private modifiers

public:

• any other class can directly access that object by name

• classes generally specified as public

• instance variables usually not public

Encapsulation

consider example of driving a car:

• we see and use the break pedal, accelerator pedal, and steering wheel - know what they di

• we do not see mechanical details of how they do their jobs

Encapsulation divides class definition into:

• class interface (tells what the class does, gives headings for public methods)

• class implementation (contains private variables, includes definitions and bodies of public and private methods)

A well encapsulated class:

• all classes, methods, instance variables, class variables, and significant portions of code are commenyed in plain, easy to understand, english

• well named variables and indentifiers

UML Class Diagrams

• contains an outline of a class

Primitive type vs class type variables

Value of primitive type stored in the memory location assigned to the variable

Variable of class type contains memory address (references) of object named by the variable

null

null is a special predefined constant that represents a memory address that does not point anywhere

Math.random()

• returns a pseudorandom double that is greater than or equal to 0 and less than 1

• 6 sided die:

• int die = (int) (6.0 * Math.random()) + 1;

Wrapper Classes

• allows programmer to have an object that corresponds to value of primitive type

• contain useful predefined constants and methods

• ex. toUpperCase

Overloading Basics

• when two or more methods have the same name within the same class

• Java distinguishes the methods by number and types or parameters

• a method’s name and number and type of parameters is called its signature

• if it cannot match a call with a defintion, then it will attempt a type conversion

• you must not overload a method where the only difference is the type of value returned

Create 2d Array

Bubble Sort

comparing and/or swapping each element until it is sorted

Selection Sort

look for smallest value, place it at the first index, then find the smallest value from the second spot to the end of the list, and place it at the second spot, continue to sorted

Insertion Sort