COP 3540 Data Structures with OOP

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

2. 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.

3. 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

4. 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, thenwe need specialized algorithms for building, retrieving, and otherwise accessing the data itself.

5. Examples of ‘Plain Facts’ • Consider a sequence of numbers – may be best represented in an array. (a physical data structure) • Assume we need to ‘search’ this sequence for a number… • An Algorithm processes this arrangement of data. • If ordered and sufficiently large: binary search • If unordered: sequential search • Performance issues can be huge: either way. • We may best ‘represent’ (model) a familyandchildren by a tree structure. (a logical data structure) • But how might we best add members to the tree? Search for members? Delete members? What are the Algorithms to process the Structure?

6. 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.

7. Know: Definitions of terms below and have an example… • Database • Record • Field • If I should ask for a definition, please recognize that an ‘example’ is NOT a definition.

8. Object Oriented Programming • Addressed two problems of procedural languages: • Lack of correspondence between the program and the realworld, (physical description vs program realization) and • The internal organization of the program. • Most real world objects have properties. • They provide certain actions or services on data. • They can carry out a task; they provide “services” for clients.

9. Examples: • Programs were (largely) ‘procedural.’ • Divided into functions, sections, paragraphs, ‘routines.’ • Data: • either ‘local’ to one construct or • ‘global’ to many. • GlobalData, No practical way to specify what methods could access a variable and others couldn’t. • Result: for global data, all data – even data not needed by particular procedures – was available to all (or most) procedures. • Recall: Call by Reference; Call by Value?? • Frequently a source of inadvertent errors!!!

10. Objects: • Encapsulate data(attributes, fields, properties) with the operations (methods, member functions) that operate on them. • Objects have some very nice properties (to be discussed throughout this course). • Only methods within an object are allowed access to data in the object. (in Java). • An object is a real world representation of a real ‘thing.’ • An object is an instantiation of a class.

11. Classes • A class is a generalization of many objects; • A class is a template; an abstraction. • Objects are merely ‘instances’ of classes. • 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(); // creates the object • therm2 = new thermostat(); // w therm1 and 2 pointing // to their respective objects. • Consider Listing 1.1 in your book as a Review:

12. // bank.java // // demonstrates basic OOP syntax class BankAccount { private double balance; // account balance public BankAccount(double openingBalance) // constructor { balance = openingBalance; } public void deposit(double amount) // makes deposit { balance = balance + amount; } 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 { public static void main(String[] args) { BankAccount ba1 = new BankAccount(100.00); // reference and acct object System.out.print ("Before transactions, "); ba1.display(); // display balance ba1.deposit(74.35); // make deposit 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)

13. 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’ { balance = openingBalance; } public void deposit(double amount) // makes deposit: four methods (“services” provided// to clients of this object. { balance = balance + amount; } 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? } public void display() // displays balance { System.out.println("balance=" + balance); } } // end class BankAccount // I require scope terminators on methods and classes. Note: object ‘encapsulates’ everything about bank account objects; ‘ informationhiding’ too.

14. …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

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

16. Inheritance and Polymorphism • Inheritance • 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 is different. • Significant facility to support extension, maintainability, and a number of other design features. •  Polymorphism is all about design, extension, and reuse.

17. You don’t need to worry about the Java – C++ similarities and features.

18. Java Library Data Structures • Super data structures, etc. in the Java API in general. • Data Structures found in java.util.* package. • We will NOT use these. • Do NOT use these for this course. • Take a look at: Java2 Platform, Standard Edition, version 1.6.2 Specification, at http://java.sun.com/j2se/1.6.2/docs/api (the third link on my web page under Course Syllabus and Very Helpful Links.) Do look this over and try some links, in case you have never done so…

19. Study: • Summary Go through this and study Questions too. • Make sure you understand these. You will see these again shortly. 

20. Questions?