COP 3540 Data Structures with OOP

1. COP 3540 Data Structures with OOP Overview: Chapter 1

2. Important Notice • I will cover several slides (but not all) in these sets of slides. I will outline those that need elaboration. • You are responsible for studying and knowing all the slide materials and the text materials. • Exams and short quizzes will be taken largely from these slides and topics brought up in class.

3. Why Data Structures and Algorithms? • Data Structures are merely different arrangements of data in primary memory or on disk, and • Algorithms are sequences of instructions that manipulate the data in these data structures in a variety of ways.

4. Examples of Some Data Structures • Many data structures: • Arrays • Linked lists • Stacks • Binary Trees • Red Black Trees • 2-3-4 Trees • Hash Tables • Heaps, etc. • Different algorithms are needed to build, search, and manipulate data stored in these various structures

5. Plain Facts: • The plain fact is that many items in nature have an ‘natural arrangement’ with their predecessor or successor element. • Think: records in a sequential file • Think: a family ‘tree’ • If • we model this naturaloccurringarrangement in the computer using some kind of datastructure that reflects the real world realities of the data and their implicit relationships, • then • we need specialized algorithms for building, retrieving, and otherwise accessing the data itself.

6. Examples of ‘Plain Facts’ Example 1 • Consider a sequence of numbers • may be best represented in an array. • We need to ‘search’ the array for a number. • An Algorithm processes this arrangement of data. • If ordered and sufficiently large: binary search • If unordered: sequential search is our only option. • (Performance issues can be huge: either way.)

7. Examples of ‘Plain Facts’ Example 2 We may best ‘represent’ (model) a familyandchildren by a tree structure. (a logical data structure) How do we add members to such a tree? How do we Search? How to delete when there are ‘descendents’ How do we best Add to a large tree? We need veryspecific Algorithms to process this structure.

8. Data Structures are NOT Created Equal • All have advantages and disadvantages. • Worst ‘algorithm’ that processes data in one data structure may be the best in other case. • Never “poo-poo” a data structure or a seemingly inefficient algorithm!

9. Know: Definitions of terms below and have an example… • Database • Record • Field (attribute) • If I should ask for a definition, please recognize that an ‘example’ (drawing or text) is NOT a definition. • A definition must be very unambiguous.

10. Object Oriented Programming • Addressed two problems of procedural languages: • Lack of correspondence between the program and the realworld, (physical description vs program realization) • The internal organization of the program. • Most real world objects have properties (attributes). • Objects provide certain actions or services on data for clients. • They can carry out a task if sent a ‘message.’

11. Examples: • Programs were (largely) ‘procedural.’ • Divided into functions, sections, paragraphs, ‘routines.’ • Data: • either ‘local’ to one construct (function or procedure) or • ‘global’ to many. • GlobalData, No practical way to specify methods that can access a variable and those that cannot. • Result: for global data, all data – even data not needed by particular procedures – was available to all (or most) procedures. • COBOL; Can do in C and others too, if not careful •  Recall: Call by Reference; Call by Value?? • Frequently a source of inadvertent errors!!! • Know these!!!

12. Objects: • Encapsulate data(attributes, fields, properties) • and • Encapsulate operations (methods, member functions) that operate on the data. • Only methodswithin an object are allowed access to data in that object. (in Java) • (if attributes are given visibility ‘private.’) • An object may be viewed as a real world representation of a real ‘thing’ or ‘noun.’ • An object is an instantiation of a class.

13. Classes • A class is a generalization of many objects; • A class is a template; an abstraction. • Objects are merely ‘instances’ of classes, but these are real and these are what we process! • We access these objects by referencing them. (References are ‘addresses’ of the objects) •  We often create references to objects first and then create the objects themselves. • e.g. • Thermostat therm1, therm2; // references • therm1 = new Thermostat(); // createstheobject • therm2 = new Thermostat(); // w therm1 and 2 pointing // to their respective objects. • Consider Listing 1.1 in your book as a Review:

14. A good ‘review’ is undertaken in the following code… 

15. // bank.java // demonstrates basic OOP syntax class BankAccount { private double balance; // account balance why private? What kind of variable is this? Why? // Who has ‘access’ to balance? public BankAccount ( double openingBalance) // constructor { balance = openingBalance; // What is a Constructor? } public void deposit ( double amount) // makes deposit { balance = balance + amount; // What is amount called? (formally) // Is this Call by Reference or Call by Value? } // end deposit // Note ‘scope terminator’ public void withdraw(double amount) // makes withdrawal { balance = balance - amount; } public void display() // displays balance { System.out.println ("balance=" + balance); } } // end class BankAccount class BankApp // Note: this class is still in the same file…. { // Where does execution start? public static void main(String[] args) { BankAccount ba1 = new BankAccount(100.00); // reference and acct object; Other ways to do this? System.out.print ("Before transactions, "); ba1.display(); // display balance What is going on here? What do you call this? ba1.deposit(74.35); // make deposit What is the 74.35 called? ba1.withdraw(20.00); // make withdrawal System.out.print ("After transactions, "); ba1.display(); // display balance } // end main() } // end class BankApp KNOW: Instance variables; local variables; static (class) variables)

16. Let’s look at the two Classes: // bank.java // // demonstrates basic OOP syntax file name or application name or package // name…(more ahead) /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// class BankAccount { private double balance; // account balance most object data is private public BankAccount(double openingBalance) // constructor Constructor never has a ‘return type’ { // in Javadoc for @params put None. balance = openingBalance; }// end constructor public void deposit(double amount) // makes deposit: four methods (“services” provided// to clients of this object. { balance = balance + amount; }// end deposit public void withdraw(double amount) // makes withdrawal // most methods (services) are { // public. When might they be private? balance = balance - amount; // What is the signature of an object? }// end withdraw public void display() // displays balance { System.out.println("balance=" + balance); }//end display() } // end class BankAccount // I require scope terminators on methods and classes. Note: object ‘encapsulates’ everything about bank account objects; ‘ informationhiding’ too.

17. …and the second class class BankApp { public static void main(String[] args) { BankAccount ba1 = new BankAccount(100.00); // create acct // what does this statement do? System.out.print("Before transactions, "); // Explain what this REALLY is! ba1.display(); // display balance // Explain generically what this really is! ba1.deposit(74.35); // make deposit // Explain generically what this really is! ba1.withdraw(20.00); // make withdrawal System.out.print("After transactions, "); // What is this statement? What does it do? ba1.display(); // display balance } // end main() } // end class BankApp Note the scope terminators Outputs: Before transactions, balance=100 After transactions, balance=154.35

18. Inheritance and Polymorphism • Had • 1. encapsulation • 2. information hiding • What is encapsulation? Examples? • What is information hiding? Examples? • Who cares??

19. Inheritance and Polymorphism • Inheritance involves • Creation of a class (subclass, derived class, child class…) from a baseclass (super class, parent, …) • Add features in subclasses (derived classes); override features in base class, etc. •  Inheritance is all about reuse!! • Polymorphism • Are different derived classes from a base class. • Methods are said to be ‘polymorphic.’ • In practice, polymorphism usually refers to referencing a method (a ‘polymorphic’ method) that will execute a different method for different objects of different derived classes all of which come from the base class. • Method name is same; • Pointer to object (and thus method body) is different. • Significant facility to support extension, maintainability, and a number of other design features. •  Polymorphism is all about design, extension, and reuse.

20. Study: • Summary Go through these materials and the study questions too. • Make sure you understand these. You will see these again shortly. 

21. Questions?