1. Introduction to Computer Science and Object-Oriented Programming
Week 11

2. Tonight
Lab 5
Chapter 8
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3. Bubble Sort Simple sort Think of regions … … next place to bubble
[0] … …
sorted
unsorted
“Bubble through the unsorted region, to place then next value to it’s correct position
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4. Bubble Sort
Compare the first two elements of the array. If the first element is larger than the second
Then swap them
Otherwise, leave them alone.
Repeat this step
for the second and third element
then the third and fourth
and so on.
At the end of the first pass the last number in the array is the largest.
Repeat for as many times as elements in the array
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5. Bubble Sort Pass
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6. Bubble Sort 11 9 17 5 12 11 9 17 5 12 9 11 5 12 17 Initial state
Begin first pass
1st pass compare pattern: 9 11 5 12 17
Begin second pass
2nd pass compare pattern:
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7. Bubble Sort 9 5 11 12 17 5 9 11 12 17 5 9 11 12 17 Begin third pass
3rd pass compare pattern: 5 9 11 12 17
Begin forth pass
4th pass compare pattern: 5 9 11 12 17
Final state
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8. Code for Bubble Sort
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9. An Optimization Propagates up in one direction but down in the other
So…
It may get sorted before final pass!
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10. With the Optimization
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11. Object Oriented Design
Two common approaches for problem solving:
Procedural Approach
Identify tasks
break down to lowest level
Object Oriented Approach
Identify objects
Identify data (instance fields)
Identify procedures (methods)

12. OOD Begins with identifying classes (objects)
Class names should be nouns
not DetermineGrade, OrderAutomobile
easy with most objects: Grade, Automobile, Coin, Customer
some classes not as easy: Scanner, MazeResultDriver
Classes should represent a single concept from the problem domain

13. Example: Student as a class
Cohesion
Cohesion
The public interface of class relates just to the class concept.
High cohesion is good when designing a class (represents a single concept)
Example: Student as a class
But poor cohesion if it ontains methods to list times when courses are offered

14. Coupling Level to which classes are dependent on each other
A class X is dependent on another class Y if a change to Y could require a change in X
Low coupling is good when designing a class

15. Categories of Classes Classes fall into 4 categories: Domain Classes
Nouns, related to problem set (e.g., Employee, CompactDisc, Time, Skier)
Represent single concept, non-programmer recognizes
Actor Classes
Verbs, related to problem set (e.g., TaxCalculator, ReportPrinter, MazeResultDriver)
Usually a process or action, often end in -er or -or

16. Categories of Classes Classes fall into 4 categories: Utility Classes
Provides reusable services across many problem sets (e.g., Math)
Typically, only static methods and constants, no instantiation
Library Classes
Provides reusable components across many problem sets (e.g., String, ArrayList)
Instantiation required, are true objects

17. Accessor / Mutator methods
Two types of methods for class:
Accessor does not change the object (instance fields)
Mutator
changes the object’s instance fields

18. Immutable Classes
Immutable class has no mutator methods (no methods can alter the value of the data in the object)
Example is String class
String newName = name.toLowerCase( );
String str2 = str1.substring(start, end);
Another example is Wrapper classes (Double, Integer)
Call to intValue( ) method of Double class does not change the value of the Double variable