CSE 501NFall ‘0901: OO Concepts + Java Basics

27 August 2009

Nick Leidenfrost

Lecture Outline Motivation

Some Terminology / History / Architecture Overview

From ideas to software Compiled Languages Interpreted Languages

Evolution of programming languages

Object-Oriented (OO) programming concepts

Basic Java Syntax

Motivation: Why am I here?

1.) You want to learn to how to program. 2.) Someone else wants you to learn how

to program. (Hopefully we can turn any #2s out there into #1s)

Even if you never intend to write a computer program after this class, you will leave with: The core knowledge base to learn and understand

almost any programming language The ability to communicate at a high level and a low

level with others about software development

Architecture of a Modern Computer(Simplified)

Faster Slower

Hard Disk(a.k.a. Hard Drivea.k.a. Virtual Memory)

Random Access Memory(a.k.a. RAMa.k.a. Main Memory)

Central Processing Unit(a.k.a. CPUa.k.a. Processor)

CPU

Cache(On-ProcessorMemory)

Registers(Very small,very fast)

The Nuts and Bolts

Bits and Bytes Who knows what a bit is?

Smallest Unit of storage 0 or 1

Who knows hat a byte is? 8 bits Capable of storing 256 distinct values

0 – 255 -128 – 127

The storage capacity of any datatype is 2^n, where n is the number of bits in the datatype

Kilobyte: 1024 bytes Megabyte: 1024 Kilobytes, 1024² bytes Gigabyte: 1024 Megabytes … etc.

A (very) Brief History of Computing

Once upon a time, shortly after the discovery of fire, people programmed in machine language (binary).

They did this on a number of punch cards that had to be fed, in order, to a computer

Programs were carried around in large boxes

Any rearrangement of these cards could cause errors in computation, extreme panic, and even death.

A (very) Brief History of Computing

Initially, programming in machine language wasn’t too bad, because memory and computing power was limited.

Advancements in hardware enable more complicated programs

Realizing that it was very difficult to program complicated procedures in machine language, we developed High-Level (a.k.a. Human Readable) Programming Languages

Evolution of Programming Languages Programming in Machine-Level Language (binary 1st Generation)

101110101010100100010101010101010100101001

Low level languages (2nd Generation) Assembly

MOV AX 2MOV BX 3ADD AX BXMOV AX CX

High level languages (3rd Generation) Procedural languages, e.g., C (Programs are comprised of a collection of

methods or functions)

int add (int a, int b) { return a+b;}

Object oriented languages, e.g., Java, C++ (Programs are comprised of a collection of interacting Objects and Classes)

Math.add(a, b);

com

pile

s in

to

Hardware Vendors Raise the Ante

PC, Mac, Sun, etc Different CPUs, Different instruction sets Different Conventions for Memory

Little-Endian / Big-Endian (where high-order bytes reside in datatypes with

multiple bytes)

Other hardware discrepancies

Compiled vs. Interpreted Languages

Compiled (C, C++, VB, etc.) Human-readable code converted directly to Machine Code (binary) Faster Not portable to other platforms

Interpreted (Java, C#) Human-readable code converted to intermediary instruction set

Common Interface Language (CIL) .class files (bytecode)

Portable

Non-compiled (scripting) Languages (Perl, PHP, Python, Javascript) Run inside of a parent application like Interpreted Languages Do not need to be compiled first, parse code just prior to runtime

Syntax / other errors usually prevent program from running Cooomparatively Slooooowwww

From Ideas to SoftwareCompiled Languages (C, C++, VB, etc.)

Code is translated directly to machine executable binary

Each binary result is specific to the type of platform (machine and OS) E.g., Mac, PC, Unix, Linux

Fast execution

No cross-platform compatibility

101001110010101011001101011111000101

101011011000010001110110111011000010101011011000101101011

If (myVar > 1) { …}else { …}

Program Design

Program Requirements

Compiler

Compiled Program

From Ideas to SoftwareInterpreted Languages (BASIC, Java, C#, etc.)

Code is translated to an interim format

An interpreter translates between the interim format and machine code

Slower execution due to translation

Cross-platform compatibility Still require platform specific interpreter

101001111001101011000100011

Interpreter

CompiledInterim Format

(.class, CIL, bytecode)

#(&$)(*&%%^$^#$%*%&(%^&*^%^&*(^&%^#$#$^&*%^&$#%^#)%$%^&*&*(&^%

If (myVar > 1) { …}else { …}

Program Design

Program Requirements

Compiler

Why Java?

Java is an interpreted Language, so bytecode (.class files) will run anywhere

Java is a high-level Object-Oriented Programming Language (OOPL)

Java has some niceties built into it that make programming easier Java has some built in “checks” that remove some of the “sharp

edges” of other programming languages Java has Memory management (a.k.a. “Garbage Collection”)

Java has a rich set of online libraries that we can use to make complicated software with relatively little work

Java was around before C# and other peers

Object-oriented ProgrammingHigh-level Entities

Class Often model real-world objects / relationships

e.g., the class Student Comprised of Fields and Methods Defines an internal state Defines methods to change its internal state

Object A specific instantiation or example of a class definition The unit of programming in OO languages Multiple objects can be created from a single class definition

Ken, Sally are both objects of the class Student

Method (or function) A means of defining the behavior of the object

May change the state of the object Is comprised of statements Accessors / Mutators / Subroutines

Field Define the state of the object

It is extremely important to be able to distinguish between classes and objects

A class defines the basic features and behavior of a certain type of entity Think of it as a Cookie Cutter

An object is a specific example of a class Objects “Ken” and “Sally are instances of the class Student Key and Sally obey the definition of the general class Student Internal states of Ken and Sally are independent

Object-oriented ProgrammingDifferentiating between Classes and Objects

class Student

Attributes:majorGPAtotalCreditscourseLoad

MethodsaddCourse() { … }getGPA() { … }removeCourse() { … }setGrade() { … }

Object-oriented ProgrammingMethods and Attributes

Kenmajor = “BME”

GPA = 3.75totalCredits = 15

courseLoad = 15

Sallymajor = “CS”

GPA = 3.0totalCredits = 33

courseLoad = 12

Instances of the class “Student”

(object)

(object)

OO Concepts: Abstraction

The act of representing essential features without including how exactly things work internally

Classes use the concept of abstraction to hide implementation details

Abstraction is very important because it allows programmers to… Write code at a higher level Not worry about implementation details of sub-modules

OO Concepts: Encapsulation

Increasing stability of a complex program by preventing access to inner workings of its internals

Restricted access means that we can maintain a valid internal state

A “Closed System” would be an extreme example Encapsulation is a principle benefit of OO Programming,

and we have various methods of promoting it

OO Concepts: Inheritance

Basic classes can be used to derive another more complex class definition Behavior is inherited by subclasses Behavior can be overridden (changed)

Allow us to reuse code (reduce duplication) Create class hierarchies

“superclass” = more generic “subclass” = more specific

Person

Student Teacher

Superclass

Subclass

is-a is-a

OO Concepts: Polymorphism

The ability to interact uniformly with objects of different classes, and have the classes define their behavior

Utilized in conjunction with inheritance to write general and abstract programming solutions

KenObject of type Student

Ron

Object of type Teacher

Person

Can both be used as…

Java Programming Basics

In the Java Programming Language:A program is made up of interacting

objects from one or more classesA class contains one or more members

(fields and methods)A method contains program statementsWe can make “notes” in our code with

the use of comments

Java Programming BasicsComments

// 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 */

/* Comments are ignored by the compiler, and are mainly to help our comprehension of the code. */

Java Programming BasicsProgram Structure

public class Calculator {

}

// comments about the class

public int add (int a, int b) {

}

// comments about the method

return a + b;

statement

statementterminator

Java Programming BasicsProgram Structure

public class Calculator {

}

// comments about the class

class header

class body

Comments can be placed almost anywhere

Java Programming BasicsProgram Structure

public class Calculator {

}

// comments about the class

// comments about the fieldprotected int answer;

Java Programming BasicsProgram Structure

public class Calculator {

}

// comments about the class

public int add (int a, int b) {

}

// comments about the method

method headermethod body

Once we learn Java…Other languages

public int add (int a, int b) {return (a + b);

}

function add ($a, $b) {return ($a + $b);

}

int Calculator::add (int a, int b) {return (a + b);

}

function add (a, b) {return Number(a) + Number(b);

}

Java

C

Javascript

PHP

C++int add (int a, int b) {

return (a + b);}

public void add (int a, int b) {return (a + b);

}

C#

Conclusion

Questions?

Lab 0 Assigned today, Due Thursday, Sept. 3rd

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Compile and Run a Java program with basic tools