An Introduction to Java and Program Design

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Chapter 1

• An Introduction to Java and Program Design

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Introduction

• A program is a step-by-step series of
  instructions for a computer
• Programming is the process of writing these
  instructions
• Programmers, or developers, design and write
  programs using a programming language or
  development tool
• Java is a programming language that provides the
  structure for efficient and economical programs

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What Is Java?

• High-level language
• Object-oriented
• Data and operations are packaged into a single
  unit called an object
• Basic syntax derived from C, C, and Smalltalk
• Designed by a team from Sun Microsystems led by
  James Gosling in the early 1990s

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What Is Java?

• Parsimonious
• Compatible with older versions
• Robust
• Strongly typed and incorruptible data
• Secure
• Protection against misuse of code
• Portable
• Platform-independent

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Java Program Types

• Console and Windowed applications
• Applets
• Servlets
• Web Services

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Console Applications

• Stand-alone programs using a command-line
  interface

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Windowed Applications

• Stand-alone programs using a graphical user
  interface (GUI)

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Applets

• Client-side programs executed within a Web browser

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Programming a Computer

• Companies need developers to build general
  application software packages
• Custom applications are built for specific needs
• Existing programs need maintenance and upgrades
• New applications will be needed due to emerging
  technologies

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• Programmers follow a general methodology called
  the program development cycle to structure the
  development process. The phases of the cycle are
• Analyze the requirements
• Design the solution
• Validate the design
• Implement the design
• Test the solution
• Document the solution

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Phase 1 Analyze Requirements

• Verify that the requirements are clear and
  complete
• Evaluate the problem to determine that it is
  solvable using a program
• List the required input and output data
• Determine whether the input data is available for
  testing

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Phase 1 Analyze Requirements

• Ensure that a solution, or algorithm, can be
  developed with the information provided in the
  requirements
• Verify the user interface specifications

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Phase 2 Design Solution

• Develop a logical model that illustrates the
  sequence of steps you will take to solve the
  problem
• Use design tools such as storyboards, object
  structure diagrams, flowcharts, and pseudocode to
  outline the logic of the program
• An algorithm is a sequence of precise
  instructions that leads to a solution
• Example Determine how many times a name occurs
  in a list of names

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Example Determine how many times a name occurs
in a list of names

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Phase 2 Design Solution

• Storyboards are sketches of the user interface

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Phase 2 Design Solution

• Flowcharts graphically represent the logic used
  to develop an algorithm
• Control structures allow the programmer to
  specify the code that will execute only if a
  condition is met
• Flowcharts use pseudocode, English, or
  mathematical notation inside symbols to represent
  the steps of a solution

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Phase 2 Design Solution

• Pseudocode is an English representation of how
  the program code should be written

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Phase 3 Validate Design

• The programmer steps through the solution with
  test data
• The user agrees that the program design solves
  the problem put forth in the requirements
• The user verifies that the initial requirements
  document contains all necessary requirements

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Phase 4 Implement Design

• Write the code that translates the design into a
  program
• Create the user interface
• Create comments within the code that explains the
  purpose of the code
• Test the code as it is written
• Test related code

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Phase 4 Implement Design

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Phase 5 Test Solution

• Create a test plan with test cases of sample
  input data and expected output
• Perform integration testing to ensure that
  components interact correctly
• Test boundary values
• Document any problems
• If results are unsatisfactory, a new iteration of
  the development cycle begins

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Phase 6 Document Solution

• Requirements documents, program design documents,
  user interface documents, and documentation of
  the code
• Test cases and proof of successful completion of
  testing
• Program code should be archived electronically

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Object-Oriented Programming and Design

• Object-oriented programming
• Data and the code that operates on the data are
  packaged into a single unit called an object
• Object-oriented design
• Identifies how objects interact with each other
  to solve a problem

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Objects

• Class
• Implementation of an object or set of objects
  with a common structure and behavior
• Class diagram
• A tool displaying a hierarchy of classes,
  including superclasses and subclasses
• Instance
• A specific occurrence of an object
• Attributes
• The properties of an individual object
• Method
• The code of an operation on the data of an object

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Operations

• Message
• The activation of an operation through naming the
  object and the operation to be performed on the
  object
• Trigger
• Impetus for a sent message
• Event
• The process of a trigger sending a message that
  results in an operation

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Event Diagrams

• Graphically represents relationships among event
  and operations
• Useful for designing event-driven programs

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Operation, message, trigger, and event

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Encapsulation

• The process of hiding the implementation details
  of an object from its user
• The user is shielded from the systems complexity
• Information hiding provides access to an object
  only through its messages
• Objects can be modified without requiring
  application modification

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Inheritance

• An efficient way to reuse code by defining a
  subclass as an extension of another class
• The subclass inherits all the data and functions
  of the superclass
• The subclass has at least one attribute or method
  that differs from its superclass

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Polymorphism

• Allows an instruction to be given to an object
  using a generalized command
• The same command will obtain different results
  depending on the object receiving the command
• The specific actions internal to the object are
  encapsulated from the user

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Abstraction

• Simplifies complex reality by modeling classes
  appropriate to the problem
• Works at most appropriate level of inheritance
  for a given aspect of the problem
• Abstraction is also achieved through composition

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Object Oriented Design

• ID classes to be written
• ID behaviors (methods) for each class
• Determine relationship between classes
• Write the interface (public method headers) for
  each class
• Implement the methods
• Many applications have similar object types
• Low level basic component(s)
• Collection of low level components
• Controlling object that puts everything together
• Display object (could be a GUI)

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Class Relationships

• IS-A inheritance
• Subclass IS-A Superclass
• Subclass extends Superclass
• Example Pencil IS-A Writing Utencil
• HAS-A composition
• ClassA HAS-A instance variable of type ClassB
• Example MixedNumber HAS-A FractionNumber
• Independent Class class that needs no other
  classes for its implementation

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Types of Development

• Bottom up implement simplest classes/methods
  first
• Methods/classes added one at a time, tested as
  you go
• A driver class (a class that is meant to run
  other methods/classes) is often used for testing
• Top down implement the highest level
  controlling object first
• Stub a dummy (empty) method used for testing
  stands in until the actual method is written

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Designing Methods

• Procedural (Functional) Abstraction using
  helper methods to cut down on repeated code
• Example reduce()
• Information Hiding declaring instance variables
  (data/attributes) and helper methods as private

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Program Analysis

• Correctness a program works for every possible
  set of test data
• Assertions a precise statement about a program
  at any given point
• If an assertion is proved to be true, then
  program is working correctly
• Precondition for any piece of code (method,
  loop, block), a statement of what is true
  immediately before execution of that code
• Postcondition for any piece of code (method,
  loop, block), a statement of what is true
  immediately after execution of that code

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Efficiency

• An efficient algorithm is economical in the use
  of
• CPU time the number of machine operations
  required to carry out the algorithm (arithmetic
  operations, comparisons, swaps, etc.)
• Memory the number and complexity of the
  variables used
• Algorithms are also graded on readability

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Example 1 Write a program that simulates a game
of Bingo. There should be at least 2 players,
each of whom has a bingo card, and a caller who
calls the numbers

• Nouns to consider
• Basic Objects
• Collection
• Controller
• Display

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Example 2 Write a program that maintains an
inventory of stock items for a small store.

• Nouns to consider
• Basic Objects
• Collection
• Controller
• Display

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Testing and Debugging

• bug
• debugging
• Kinds of Errors
• Syntax/Semantic error compilation errors
• Run-time error
• Logic error
• Error message vs. warning message

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What Is the Java SDK?

• The Java Software Development Kit (SDK) is a
  programming package to develop Java applications
• The Java Runtime Environment (JRE) provides the
  tools to deploy Java applications

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Features of the Standard Edition

• The Java Compiler
• Converts code into bytecode
• The Java Virtual Machine
• Contains an interpreter to execute the bytecode
• The Java API
• The standard set of packages available in Java
• java.sun.com
• The Java Applet Viewer
• Mini browser to display Java applets

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Other Java Development Tools

• VATE (value-added text editor)
• Color codes elements and numbers lines
• Examples TextPad, Eclipse, Visual Studio

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What is computer hardware?

• Computer hardware are the physical components of
  the computer.

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Input/Output Devices

• Input/Output devices provide communication
  between user and hardware.
• Input Devices
• Keyboard
• Mouse
• Scanner
• Output Devices
• Monitor
• Speakers
• Printer

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Processors and Memory

• Central Processing Unit (CPU)
• Performs basic functions, millions and billions
  of times per second (brains of the computer)
• Random-Access Memory
• Stores data used by the CPU (before and after
  processing)

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Data Storage

• Data storage uses a variety of media. Capacity
  is measured in bits and bytes
• A bit represents the on or off state of a
  transistor (symbolized by a 1 or a 0).
• A byte is eight bits.
• A kilobyte is 210 or 1,024 bytes.
• A megabyte is 1,048,576 bytes.

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Hard Drives

• The hard drive is the primary storage device in
  a computer. Hard drives are
• Long term, rewritable storage
• Large capacity
• Inexpensive
• Fixed media (relatively difficult to move from
  one computer to another)

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Removable Media

• Some storage devices are more portable
• CD/DVD
• Medium capacity
• Inexpensive
• Easy to transport from one computer to another
• Flash, Zip, USB drives
• Differing capacities
• Differing price per MB

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Computer Software

• Software can be divided into two categories
• Systems software includes operating systems,
  compilers, and utilities.
• Application software runs on top of an operating
  system.

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What is an operating system?

• An operating system (OS) manages the hardware
  and software on a computer system. An OS
• Manages memory and hardware resources
• Allocates resources to applications
• Provides a consistent interface for applications

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Operating Systems

• UNIX/Linux
• Multiuser OS
• Multitasking
• Runs on many types of hardware
• Modular tools
• Mac OS
• First mainstream graphical user interface
• Icons (pictures) and mouse replaced command line
  interface
• DOS/Windows
• DOS gained popularity with first PCs
• Windows provided graphical interface to DOS
• Windows later separated itself from DOS
  underpinnings

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Low-Level Languages

• Low-level programming languages use simple
  commands to communicate with the CPU
• Machine language (most basic language of the CPU)
• Assembly language (human readable, but close to
  machine language)

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High-Level Languages

• High-level languages can be procedural or
  object-oriented
• Procedural languages use a step-by-step process
  to solve a problem.
• Basic, Pascal, C
• Object-oriented languages model problems using
  objects that correspond to real-world
  counterparts.
• Smalltalk, C, Java