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Chapter 1 Introduction to Object- Oriented Programming and Problem Solving.

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1 Chapter 1 Introduction to Object- Oriented Programming and Problem Solving

2 2 Knowledge Goals Understand what a computer program is Know the three phases of the software life cycle Understand what an algorithm is Learn what a high-level programming language is Understand the difference between machine code and Bytecode

3 3 Knowledge Goals Understand the compilation, execution, and interpretation processes Learn what the major components of a computer are and how they work together Understand the concept of an object in the context of computer problem solving

4 4 Skills Goals List the basic stages involved in writing a computer application Distinguish between hardware and software List the ways of structuring code in a Java application Name several problem-solving techniques Choose an applicable problem-solving technique Identify the objects in a problem statement How can you distinguish the knowledge goals from the skills goals?

5 5 What is Programming? Computer A programmable device that can store, retrieve, and process data Computer programming The process of specifying objects and the ways in which those objects interact to solve problems Programming Writing out instructions for solving a problem or performing a task Computer program Instructions defining a set of objects and orchestrating their interactions to solve a problem

6 6 How do we write a Program? Water- fall Model

7 7 How do we write a program … Problem-Solving Phase Understand (define) the problem and identify what the solution must do Specify the objects and their interactions to solve the problem Follow the steps exactly to see if the solution really does solve the problem

8 8 How do we write a program … Implementation Phase Translate the object specifications (the general solution) into a programming language Have the computer carry out the solution and check the results What if the solution isn't correct?

9 9 How do we write a program … Maintenance Phase Use the program Modify the program to meet changing requirements, to enhance its functionality, or to correct any errors that show up in using it

10 10 How do we write a program … Can't we shorten the process ?

11 11 How can a computer work with objects? Information Any knowledge that can be communicated Data Information in a form that a computer can use Object A collection of data values and associated operations How does all this fit together?

12 12 How can a computer work with objects… Data with related operations represents information as objects

13 13 How can a computer work with objects… Objects contain data and operations Consider a Name object What sort of data would this object contain? What sort of operations might we need to manipulate the data?

14 14 How can a computer work with objects… What other operations might we want ?

15 15 Classes of Objects What about multiple objects with the same properties? Class A specification of the representation of a particular kind of object, in terms of data and behavior (operations)

16 16 Classes of Objects Date class data: month, day, year operations: set and return month, day, year Date object (an instance of a class) June 23 2004

17 17 What is an algorithm? How are the operations specified? Algorithm Instructions for solving a problem in a finite amount of time using a finite amount of data

18 18 What is an algorithm? Objects: Key, Transmission, Gas Pedal, Engine, Phone 1. Insert the key. 2. Make sure the transmission is in Park (or Neutral). 3. Depress the gas pedal. 4. Turn the key to the start position. 5. If the engine starts within six seconds, release the key. 6. If the engine doesn’t start within six seconds, release the key and gas pedal, wait ten seconds, and repeat Steps 3 through 6, but not more than five times. 7. If the car doesn’t start, phone your mechanic.

19 19 What is an algorithm? Once we have the algorithm, then what? We translate the algorithm into statements in a programming language Say again?

20 20 What is a programming language? Programming language A set of rules, symbols and special words used to construct a computer program Statements Specific combinations of symbols and special words that are defined by a programming language to be complete units within a program; analogous to sentences in a human language Code Instructions for a computer that are written programming language

21 21 What is a programming language? There is no single way to implement an algorithm

22 22 What kind of instructions … Computer A programmable device that can store, retrieve, and process data Implies accept data, send data, perform arithmetic operations, perform logical operations

23 23 What kind of instructions … Control structures Statements that organize the instructions that specify the behaviors of objects -sequence -selection -repetition -subprograms -asynchronous

24 24 What kind of instructions …

25 25 What kind of instructions …

26 26 Software Maintenance Maintaining software accounts for the majority of its live cycle (i.e., old programs never die, they just get modified) Where were you on January 1, 2000?

27 27 Software Maintenance Software maintenance tips -Check existing code -Make changes to a copy -Change related aspects to leave clean, consistent code for next change -Keep backup copies Software maintenance is not glamorous but it is necessary!

28 28 How It All Works Machine language The language, made up of binary-coded instructions, that is used directly by the computer Assembly language A low-level programming language in which a mnemonic represents each machine language instruction for a particular computer

29 29 How It All Works High-level language: R1 = R3 + R5 R2 = R6 - R1

30 30 How It All Works Levels of abstraction

31 31 Machine Language Is not portable Runs only on specific type of computer Is made up of binary-coded instructions (strings of 0s and 1s) Is the language that can be directly used by the computer Why is portability important?

32 32 Assembly Languages Are machine dependent and run on only one specific type of computer Are translated into machine code by assemblers Are made up of English-like abbreviations such as LOAD, STORE, or ADD Better than machine language…

33 33 High-Level Languages Are portable Are translated into machine code by compilers Instructions are written in language similar to natural language Examples -- FORTRAN, COBOL, Pascal, C, C++ Many are standardized by ISO/ANSI to provide an official description of the language

34 34 High-Level Languages Source code Instructions written in a high-level language Object code A machine language version derived from source code

35 35 Portability Compiler portability

36 36 Java's Road to Portability Bytecode A standardized machine language into which Java source code is compiled

37 37 High-Level Languages Direct execution The process by which a computer performs the actions specified in a machine-language program Interpretation The translation, while a program is running, of non- machine language instructions (such as Bytecode) into executable operations Virtual machine A program that makes one computer act like another

38 38 High-Level Languages Do you understand the difference between C++ & Java portability?

39 39 What's inside the computer? Can you name any external devices ?

40 40 What's inside the computer? Memory unit Internal data storage inside a computer, made up of an ordered sequence of addressable cells Addressable?

41 41 What's inside the computer? Executes instructions The Manager Does operations Holds data and instructions

42 42 What's inside the computer? Hardware The physical components of a computer Software Computer programs; the set of all programs available on a computer Clock An electrical circuit that sends out a train of pulses to coordinate the actions of the computer's hardware components; its speed is measured in hertz (cycles per second)

43 43 What is system software? User/computer interface A connecting link that translates between the computer's internal representation of data and representations that humans are able to work with Interactive system A system that supports direct communication between the user and the computer System software The set of programs that simplifies the user/ communication interface Operating system Set of programs that manages all the computer's resources

44 44 What is system software? See how it all fits together ?

45 45 Problem Solving Problem solving The act of finding a solution to a perplexing, distressing, vexing, or unsettled question How do you define problem solving?

46 46 Problem Solving How to Solve It: A New Aspect of Mathematical Method by George Polya "How to solve it list" written within the context of mathematical problems But the list is quite general We can use it to solve computer related problems!

47 47 Problem Solving How do you solve problems? Understand the problem Devise a plan Carry out the plan Look back

48 48 Problem-Solving Techniques Ask questions! -What do I know about the problem? -What is the information that I have to process in order the find the solution? -What does the solution look like? -What sort of special cases exist? -How will I recognize that I have found the solution?

49 49 Problem-Solving Techniques Never reinvent the wheel! Similar problems come up again and again in different guises A good programmer recognizes a task or subtask that has been solved before and plugs in the solution Can you think of two similar problems?

50 50 Problem-Solving Techniques Look for familiar things

51 51 Problem-Solving Techniques Solve by analogy

52 52 Problem-Solving Techniques Means-end analysis

53 53 Problem-Solving Techniques Divide and conquer

54 54 Problem-Solving Techniques Building-block approach

55 55 Problem-Solving Techniques Merging solutions

56 56 Problem-Solving Techniques Object-Oriented Problem Solving Stages -Brainstorm List all objects that might contribute to solution -Filter Review the classes to find duplicates or remove unnecessary objects -Responsibilities Determine the operations associated with a class of objects -Collaborations Determine the interactions between classes

57 57 Problem-Solving Techniques -Attributes Determine the values defined by a class that are used to represent its objects -Driver Write a program for creating the objects and coordinating their collaborations to solve the problem

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