Chapter 1: Object Oriented Paradigm

1. Chapter 1: Object Oriented Paradigm

2. 1.1 Data Abstraction and Encapsulation • OOP allows programmer to • separate the details that are important to the user • myCoin.flip(); myCoin.getValue(); • from the details that make the abstraction work • if (Math.random() > 0.5) side = "heads"; else side="tails"; • Accomplished by organizing code into • Interface: details important to user • Implementation: “unimportant” details hidden from user • Who is "user?" • person who writes the application…and/or…YOU !

3. Strings represented on Macs vs Linux

4. 1.2 The Object Model • A convenient design method • program data managed by objects • objects manage internal data, determines state • point object manages its x,y coordinates • coin object manages its side indicator • student record object manages it's name, ID, GPA • this helps manage chaos as complexity grows • reduces unexpected linkages between parts of program

5. Primary focus of class • how we implement and evaluate objects with methods that are logically complex • how we can use the objects we create • objects mainly will be data structures, • our primary interest! • occasionally we will develop control structures that manipulate other objects

6. 1.3 Object-Oriented Terminology • Applied to a Ratio class – see Demo1 in mod1 download • encapsulation • object • instance • class • fields • methods • constructor • utility methods (reduce, gcd) • static methods (gcd)

7. 1.4 A Special-Purpose Class: A Bank Account • Manages data: • balance and account number (or account name) • Performs: • getAccount • getBalance • deposit • withdraw

8. BankAccount equals() method public boolean equals(Object other) // pre: other is a valid bank account // post: returns true if this bank account is the same as other { BankAccount that = (BankAccount)other; // two accounts are the same if account numbers are the same return this.account.equals(that.account); }

9. Class Object • Every class is a descendant of Object • Defines fundamental methods • equals() same data as another object • toString() string representation for display • clone() makes an identical copy • If you don't define your own versions of these, automatic (usually defective) ones will be provided

10. Memory Model of BankAccount object BankAccountjane; jane = new BankAccount(“J. Doe”, 345.67); Memory allocated by the declaration BankAccountjane; jane= new BankAccount(“J. Doe”, 345.67); null100 jane The number 100 indicates the memory location where the object resides account J. Doe balance 345.67

11. Shallow vs Deep Copy • There are two ways to “copy” an object • Deep copy creates a clone of the object • The objects data values are copied into the clone • Shallow copy creates reference to the object • The location of the object is copied into a reference variable • After a • Deep copy, two distinct objects exist • Can change one object’s data without changing the other’s • Shallow copy two references to one object exists

12. Code of Shallow and Deep Copies • Shallow copy is similar to copying primitives jon = jane; • Deep copy • requires a class method (e.g., in the BankAccount class) public BankAccountclone() { BankAccount copy = new BankAccount(); copy.account = account; copy.balance= balance; return copy; } • Invoked as jon = jane.clone(); //copy jane into jon

13. jon jane 100 200 location 100 location 200 account account jon j. doe j. doe deep copy balance balance 187.95 345.67 345.67 A Deep Copy of the Object jane into the Object jon Memory Model of Two Types of Copies jon jane shallow copy 100 200 200 location 200 j. doe 345.67 A Shallow Copy of the Object jane into the Object jon

14. Using Scanner and File • Scanner – a class representing objects that read input streams or files and extracts primitive data types from them • File – a class representing a path to a location on disk or other media • We will now apply these to our BankAccount app

15. 1.5 A General-Purpose Class: An Association • very general class represents a connection between two kinds of objects protected Object theKey; // the key of the key-value pair protected Object theValue; // the value of the key-value pair • Association can be used to link • ID (key) with an employee record • Two words from different languages (pig latin) • Methods: setValue, setKey, getValue, getKey

16. Protected vs Private • Usually, it is best to restrict methods as much as possible. • private: member is only used within class itself • protected: member is available to other classes in a package or to subclasses through inheritance • public: member is available to any user

17. An app that uses Association • atinLay – a Pig Latintranslator • This program uses the argument list set up in main, as would be obtained from a “command line” execution • We (or you!) could convert it to read from the System.in console with a Scanner object

18. 1.6 Sketching an Example: A Word List • Suppose we want to develop a Hangman app • The program should : • Select a random word from a list of words (TODO!) • Receive user guesses and draw stick figure (demo) • We propose to develop a WordList class to help us with item number 1) • BTW this is a “Data Structure” • How do we design such a thing????

19. 5 Step Data Structure Design Process

20. Sketch an example test applicationhelps familiarize operations needed

21. Sketch the “interface” for the classnames of methods, parameters, return types

22. Develop the implementation • Choose an internal representation • An array of words? • Write the methods • Test and debug using tester class • Then write the complete implementation