IST 311

1
IST 311 Object-Oriented Design Software

• Steven Haynes
• IST 311 Class 4
• 19 January 2006
• shaynes_at_ist.psu.edu

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Mid-Term Deliverables

• Use Case diagrams
• Derived from scenarios
• Class diagram
• Conceptual
• Sequence diagrams TBD
• Need use cases first
• User Interface Design
• Need use cases first
• Due Thursday, March 3rd (Thursday before break)

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Design Representations

• Why learn the UML?
• What is the purpose of design representation
  languages and techniques?

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Design Representations

• An aid to design cognition
• A common language for communicating about a
  design (specifications)
• A record of the design process and its outcomes
  (documentation)

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UML Diagrams, Part 1.

• Use Case diagram

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UML Diagrams

• Use Case diagram
• Identify major services provided by a system to
  external actors (users and other systems)
• Establish the boundaries of the system
• Identify common functionality
• Identify high-level alternate use scenarios
• Capture requirements
• Development project planning tasks
• Communicate with the customer/user.

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Use Case Diagram
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Use Cases

• Actors
• Use Cases
• Include (Uses) Use Cases
• Extend Use Cases
• Annotations
• Pre-conditions
• Post-conditions
• Constraints
• Dont use actor or use case generalization

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Guidelines for Use Cases

• Actors specific user roles
• Human actors on left
• Non-human actors (systems) on right
• Use Cases verb-noun phrase
• e.g., Verify Credit Card
• Include (uses) link included use case MUST be
  completed for the including use case to complete
• Extend link extending use case represents a
  variant of the extended use case

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Guidelines for Use Cases

• Use cases model system interactions.
• Use case granularity THE big problem
• Use annotations (notes) freely to document your
  assumptions.
• Use cases are not data stores
• Use cases are not data flow diagrams

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UML Diagrams

• Class diagram

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UML Diagrams

• Class diagram
• Identify classes
• Attributes
• Operations
• Identify class relationships
• Identify packages
• Describe a systems static structure

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Class Diagram
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UML Diagrams

• Sequence diagram

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UML Diagrams

• Sequence diagram
• Describe the sequence of steps required to
  realize a use case or use case scenario, which
  represent requirements
• Describe interactions between objects/classes
• Perspective is time oriented

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Sequence Diagram
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UML Diagrams

• Collaboration diagram

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UML Diagrams

• Collaboration diagram
• Same as Sequence diagram except
• Perspective is structural or spatial

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Collaboration Diagram
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Degree Audit Use Cases Classes
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Practice Exploratory Learning!

• Read Raposa chapters with a Java development
  environment at hand
• Experiment with his or your own code fragments to
  ensure you understand a given point

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Code Comments, Diagram Annotations

• Always comment your code
• Always annotate diagrams
• Most points are lost on assignments and projects
  because of clarity issues. Comments and
  annotations help overcome these problems.

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Important from Chapters 1-3

• Ch. 1
• The JVM
• Bytecodes
• Classes vs. Objects
• .java vs. .class files
• Command-line arguments
• The main method
• Ch. 2
• Java keywords
• Java identifiers
• Primitive data types
• Declaring, initializing, assigning variables

• Java Strings
• Reference vs. primitive data
• Constants
• Operators
• Comments
• Ch. 3
• Java control structures
• Boolean operators and logic

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Assumptions

• You know what data types are and can select the
  appropriate type from those available in Java
• You know what Java keywords are and can find and
  use them appropriately
• You can declare, initialize, and use Java
  variables and constants

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Assumptions Continued

• You know what operators are and can use them
• Logical AND (), OR (), EXCLUSIVE-OR () and
  NOT (!)
• Arithmetic Addition (), Subtraction (-),
  Multiplication (), Division (/), Modulus ()
• Increment (e.g., i, i), Decrement (e.g., k--,
  --k)
• Assignment (, , -, , /, )
• Relational (, lt, gt, lt, gt, !)
• You know how to use the different Java comment
  types

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Classes and Objects

• Whats the difference?

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Classes and Objects

• A class is a blueprint or template for creating
  objects and defines
• An objects attributes
• An objects behaviors (methods)
• An object is an instance of a class
• To create objects we instantiate a class

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Java Strings

• A string is a collection of character (char)
  data. Strings are important data structures in
  any programming language
• A java.lang.String object is a sequence of
  characters plus a collection of methods for
  manipulating strings.
• Unlike other Java objects, Strings have certain
  characteristics in common with the primitive data
  types.
• For example, strings can have literals. A String
  literal  is a sequence of zero or more characters
  contained in double quotes -- for example,
  Socrates and (empty string). 

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Java Strings

• The symbol is used as a binary concatenation
  operator for Strings. It has the effect of
  joining two strings together.
• Primitive types are automatically promoted to
  strings when mixed with concatenation operators.
• The number of characters in a string is its
  length.
• The position of a character within a string is
  called its index. Strings are zero indexed --
  the first character is at index 0.
• The String.valueOf() methods are class methods
  that convert primitive types into String
  objects.
• The indexOf() method searches from left to right
  within a String for either a character or a
  substring.

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Java Strings

• Methods for comparing strings
• public boolean equals(Object anObject) //
  Overrides Object.equals()
• public boolean equalsIgnoreCase(String
  anotherString)
• public int compareTo(String anotherString)
• Two strings are equal if they have the same
  letters in the same order
• String s1 "hello"
• String s2 "Hello"
• s1.equals(s2) // false
• s1.equals("hello) // true
• Error Using to compare two strings. For
  objects, o1 o2 means o1 and o2 are identical.

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Java Strings

• Java Strings cannot be modified. Whenever you
  assign a new value to a String, Java must create
  a new String object and discard the old one.
• Objects of java.lang.StringBuffer class are
  strings that can be modified.

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Java Strings

• A StringTokenizer breaks a string into tokens
  separated by delimiters, which by default value
  are the whitespace characters
• StringTokenizer sTokenizer
• new StringTokenizer("This is an English
  sentence.")
• This
• is
• an
• English
• sentence.

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Control Structures

• Sequence --- The statements in a program are
  executed in sequential order unless their flow is
  interrupted by one of the following control
  structures.
• Invoke or Call a Method --- Invoking a method
  transfers control temporarily to a named method.
  Control returns to the point of invocation when
  the method is completed.
• Decision/Selection--- The if, if/else, and switch
  statements are branching statements that allow
  choice by forking of the control path into two
  or more alternatives.
• Repetition --- The for, while, and do-while
  statements are looping statements that allow the
  program to repeat a sequence of statements.

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Control Structures

• No matter how large or small a program is, its
  flow of control can be built as a combination of
  these four structures.
• Note that each structure has one entry and one
  exit.

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Repetition

• Repetition structure a control structure that
  repeats a statement or a sequence of statements.
• A counting loop can be used if you know in
  advance how many iterations are needed. The for
  statement is used for counting loops.
• A while structure should be used if the loop body
  may be skipped entirely. The while statement is
  used.
• A do-while structure should be used only if a
  loop requires one or more iterations. The
  do-while-statement should be used.

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Loop Elements

• The loop variable, which is used to specify the
  loop entry condition, must be initialized to an
  appropriate value and updated on each iteration.
• A loop's bound, which may be a count, a sentinel,
  or, more generally, a conditional bound, must be
  correctly specified in the loop-entry expression,
  and progress toward it must be made in the
  updater.
• An infinite loop may result if either the
  initializer, loop-entry expression, or updater
  expression is not correctly specified.

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Homework Assignment

• This is an individual assignment.
• Read Raposa Chapter 4.
• Using Eclipse, write a Java class for each of the
  classes you designed for homework 2.
• Write another class (a program), the main class
  with the main() method, that creates an instance
  of each of these classes, then calls one method
  in each to output the method name.
• Due at the start of class Tuesday, 1/24.
• Hand in hard copies of the object definitions
  (classes) and of the source code.