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Chapter 8 Slides

Exposure Java 2011 PreAPCS Edition. Chapter 8 Slides. Introduction to OOP. PowerPoint Presentation created by: Mr. John L. M. Schram and Mr. Leon Schram Authors of Exposure Java. Section 8.2. OOP. A Gentle. First Exposure. OOP.

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Chapter 8 Slides

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  1. Exposure Java 2011 PreAPCS Edition Chapter 8 Slides Introduction to OOP PowerPoint Presentation created by: Mr. John L. M. Schram and Mr. Leon Schram Authors of Exposure Java

  2. Section 8.2 OOP A Gentle First Exposure

  3. OOP Object Oriented Programming (OOP) is a style of programming that incorporates these 3 features: Encapsulation Polymorphism Inheritance Object Oriented Programming simulates real life by using a program style that treats a program as a group of objects.

  4. OOP Example A car could be an object in Java. Objects have attributes and methods. Nouns Verbs

  5. Encapsulation Encapsulation means packaging or encapsulating all of the attributes and methods of an object in the same container.

  6. Polymorphism If we review our Algebra we should remember: A monomial is a single term like: 3x A binomial is 2 terms like: 3x + 7 A polynomial is many terms like: x2 + 3x + 7 The prefix Poly means many. Polymorphism means many forms. Polymorphism is an advanced concept in computer science which will be discussed in AP Computer Science. To attempt to explain it now will only cause confusion.

  7. Inheritance Suppose you wish to create Truck objects, Limo objects and Racecar objects. Instead of starting each from scratch we can use the existing Car in the following manner: Inheritance will be discussed in Chapter 9. A Truck is a Car with 4WD, big tires, and a bed. A Limo is a very long luxury Car with many seats. A Racecar is a Car with 1 seat, a very powerful engine, and a number painted on the side.

  8. Section 8.3 Encapsulation and Reliability

  9. The 4 Stages of Program Design  Cryptic Programming Stage  Unstructured, Spaghetti-Programming Stage  Structured Programming Stage  Object Oriented Programming Stage

  10. Avoid Spaghetti Programming Program Statement Program Statement Program Statement Program Statement Program Statement Program Statement Program Statement Program Statement

  11. Back to Encapsulation Java encapsulates data and action modules that access the data in one container, called an object. Object members that perform some task are called methods. Object members that store data are called attributes.

  12. The Airport Analogy

  13. Normal “Non-OOP” Airport • In a normal airport, the following places are scattered all over the airport. • Curb-Side Check-In • Security • Departure Gates • Arrival Gates • Baggage claim • The same gates are used for the arrival and departure of different planes to different places.

  14. “OOP-ified” Airport An airport would never be designed this way, but if they followed the encapsulation concept of OOP, you would have the following Destination objects: class Destination object Paris Methods: Check-In Security Gates class Destination object Amsterdam Methods: Check-In Security Gates

  15. Section 8.4 The Bank class from Scratch

  16. // Java0801.java // Stage #1 of the <Bank> class // The only thing that is done in this stage is the creation of a container. // It is the "container" or "block" or officially the "class" which will be the // toolkit for all the different tool necessary to handle bank transactions. // This <Bank> class is minimal program code. It does nothing, but it will compile. // The <Java0801> class contains the <main> method used to test our user-created class. public class Java0801 { public static void main(String args[]) { System.out.println("\nJAVA0801.JAVA\n"); } } class Bank // The class heading of the <Bank> class { // The opening brace of the <Bank> container // All elements of the <Bank> must be placed // between the braces } // The closing brace of the <Bank> container

  17. // Java0802.java // Stage #2 of the <Bank> class // In the second stage the main method creates a <Bank> object, // called <tom>. Java does not complain. // A pretty much useless <tom> object is created. public class Java0802 { public static void main(String args[]) { System.out.println("\nJAVA0802.JAVA\n"); Bank tom = new Bank(); } } class Bank { }

  18. // Java0803.java // Stage #3 of the <Bank> class // This program may seem logical. Values are assigned to program variables. // The data variables are inside the <tom> class container. // The object.identifier syntax seems as it was shown in previous chapters. //////////// THIS IS BAD OLD-STYLE PROGRAMMING ////////// public class Java0803 { public static void main(String args[]) { System.out.println("\nJAVA0803.JAVA\n"); Bank tom = new Bank(); tom.checkingBal = 1000.00; tom.savingsBal = 3000.00; System.out.println("Checking Balance: " + tom.checkingBal); System.out.println("Savings Balance: " + tom.savingsBal); System.out.println("\n\n"); } } class Bank { double checkingBal; // data attribute to store the object's checking balance double savingsBal; // data attribute to store the object's savings balance } The way this program is written, nothing prevents Tom from changing his balances to $1,000,000 or more. Nothing prevents someone else from changing it to $0.00 as well.

  19. // Java0804.java // Stage #4 of the <Bank> class // This protects the checking and savings balances from // outside alteration by making them private attributes. public class Java0804 { public static void main(String args[]) { System.out.println("\nJAVA0804.JAVA\n"); Bank tom = new Bank(); tom.checkingBal = 1000.00; tom.savingsBal = 3000.00; System.out.println("Checking Balance: " + tom.checkingBal); System.out.println("Savings Balance: " + tom.savingsBal); System.out.println("\n\n"); } } class Bank { private double checkingBal; // data attribute to store the object's checking balance private double savingsBal; // data attribute to store the object's savings balance }

  20. private & public Members Members in a class need to be declared as private or public. private members cannot be accessed by any program segments outside the class. public members of a class can be accessed by program segments outside the class. Class attributes are usually declared private. Class methods are usually declared public.

  21. // Java0805.java // Stage #5 of the <Bank> class // This stage adds a "constructor" method, which initializes the both balances to zero. // The constructor is automatically called when the new object (line 12) is constructed. // There is no output, because data is assigned, but not displayed. public class Java0805 { public static void main(String args[]) { System.out.println("\nJAVA0805.JAVA\n"); Bank tom = new Bank(); System.out.println("\n\n"); } } class Bank { // The attributes (data variables) are usually listed first inside the class container. private double checkingBal; private double savingsBal; // The methods (modules that process attributes) usually start with the constructor. // The constructor has the same name as the class and initializes the data variables. public Bank() { checkingBal = 0.0; savingsBal = 0.0; } }

  22. Instantiation& Construction A class is a template that can form many objects. An object is a single variable instance of a class. Objects are sometimes called instances. An object is created with the new operator. The creation of a new object is called: instantiation of an object construction of an object The special method that is called during the instantiation of a new object is the constructor.

  23. // Java0806.java Stage #6 of the <Bank> class // Two methods are added to access the attribute values for public use. // It is now possible to see the balances of the bank account. public class Java0806 { public static void main(String args[]) { System.out.println("\nJAVA0806.JAVA\n"); Bank tom = new Bank(); System.out.println("Checking Balance: " + tom.getChecking()); System.out.println("Savings Balance: " + tom.getSavings()); System.out.println("\n\n"); } } class Bank { private double checkingBal; private double savingsBal; // The methods (modules that process attributes) usually start with the constructor. // The constructor has the same name as the class and initializes the data variables. public Bank() { checkingBal = 0.0; savingsBal = 0.0; } // The next two methods are "read-only" methods that return private data values. // Such methods are traditionally called "get methods" and "get" is often in the name. public double getChecking() { return checkingBal; } public double getSavings() { return savingsBal; } }

  24. “Mr. Schram, how does using private give you any security when you can just change it back to public?” Think of any video game that you have ever purchased. Do you ever see the source code? Only the programmers have the source code. What they sell to users is an executable file.

  25. // Java0807.java Stage #7 of the <Bank> class // This stage demonstrates how to create an "overloaded" method. The 2nd constructor has the same // identifier as the 1st constructor. However, the second constructor has a different heading signature. // Java knows which method to use by checking the parameters. A 2nd constructor allows user-input // for the constructor. This program also shows that is it possible to have two bank accounts. // This is only possible with a class that has object methods. public class Java0807 { public static void main(String args[]) { System.out.println("\nJAVA0807.JAVA\n"); Bank tom = new Bank(); Bank sue = new Bank(2000.0,2000.0); System.out.println("Tom's Checking Balance: " + tom.getChecking()); System.out.println("Tom's Savings Balance: " + tom.getSavings()); System.out.println(); System.out.println("Sue's Checking Balance: " + sue.getChecking()); System.out.println("Sue's Savings Balance: " + sue.getSavings()); System.out.println("\n\n"); } } class Bank { /////////// ATTRIBUTES ////////// private double checkingBal; private double savingsBal; ////////// CONSTRUCTOR METHODS ////////// public Bank() { checkingBal = 0.0; savingsBal = 0.0; } public Bank(double cBal, double sBal) { checkingBal = cBal; savingsBal = sBal; } } Only new methods are shown.

  26. // Java0807.java Stage #7 of the <Bank> class // This stage demonstrates how to create an "overloaded" method. The 2nd constructor has the same // identifier as the 1st constructor. However, the second constructor has a different heading signature. // Java knows which method to use by checking the parameters. A 2nd constructor allows user-input // for the constructor. This program also shows that is it possible to have two bank accounts. // This is only possible with a class that has object methods. public class Java0807 { public static void main(String args[]) { System.out.println("\nJAVA0807.JAVA\n"); Bank tom = new Bank(); Bank sue = new Bank(2000.0,2000.0); System.out.println("Tom's Checking Balance: " + tom.getChecking()); System.out.println("Tom's Savings Balance: " + tom.getSavings()); System.out.println(); System.out.println("Sue's Checking Balance: " + sue.getChecking()); System.out.println("Sue's Savings Balance: " + sue.getSavings()); System.out.println("\n\n"); } } class Bank { /////////// ATTRIBUTES ////////// private double checkingBal; private double savingsBal; ////////// CONSTRUCTOR METHODS ////////// public Bank() { checkingBal = 0.0; savingsBal = 0.0; } public Bank(double cBal, double sBal) { checkingBal = cBal; savingsBal = sBal; } } Default (no-parameter) Constructor

  27. // Java0807.java Stage #7 of the <Bank> class // This stage demonstrates how to create an "overloaded" method. The 2nd constructor has the same // identifier as the 1st constructor. However, the second constructor has a different heading signature. // Java knows which method to use by checking the parameters. A 2nd constructor allows user-input // for the constructor. This program also shows that is it possible to have two bank accounts. // This is only possible with a class that has object methods. public class Java0807 { public static void main(String args[]) { System.out.println("\nJAVA0807.JAVA\n"); Bank tom = new Bank(); Bank sue = new Bank(2000.0,2000.0); System.out.println("Tom's Checking Balance: " + tom.getChecking()); System.out.println("Tom's Savings Balance: " + tom.getSavings()); System.out.println(); System.out.println("Sue's Checking Balance: " + sue.getChecking()); System.out.println("Sue's Savings Balance: " + sue.getSavings()); System.out.println("\n\n"); } } class Bank { /////////// ATTRIBUTES ////////// private double checkingBal; private double savingsBal; ////////// CONSTRUCTOR METHODS ////////// public Bank() { checkingBal = 0.0; savingsBal = 0.0; } public Bank(double cBal, double sBal) { checkingBal = cBal; savingsBal = sBal; } } Overloaded Constructor

  28. // Java0807.java Stage #7 of the <Bank> class // This stage demonstrates how to create an "overloaded" method. The 2nd constructor has the same // identifier as the 1st constructor. However, the second constructor has a different heading signature. // Java knows which method to use by checking the parameters. A 2nd constructor allows user-input // for the constructor. This program also shows that is it possible to have two bank accounts. // This is only possible with a class that has object methods. public class Java0807 { public static void main(String args[]) { System.out.println("\nJAVA0807.JAVA\n"); Bank tom = new Bank(); Bank sue = new Bank(2000.0,2000.0); System.out.println("Tom's Checking Balance: " + tom.getChecking()); System.out.println("Tom's Savings Balance: " + tom.getSavings()); System.out.println(); System.out.println("Sue's Checking Balance: " + sue.getChecking()); System.out.println("Sue's Savings Balance: " + sue.getSavings()); System.out.println("\n\n"); } } class Bank { /////////// ATTRIBUTES ////////// private double checkingBal; private double savingsBal; ////////// CONSTRUCTOR METHODS ////////// public Bank() { checkingBal = 0.0; savingsBal = 0.0; } public Bank(double cBal, double sBal) { checkingBal = cBal; savingsBal = sBal; } }

  29. Constructor Notes Constructors are methods, which are called during the instantiation of an object with the new operator. The primary purpose of a constructor is to initialize all the attributes of newly created object. Constructors have the same identifier as the class. Constructors are neither void methods nor are they return methods. They are simply constructors. Constructors are always declared public. Constructors can be overloaded methods. The method identifier can be the same, but the method signature (which is the parameter list) must be different. A constructor with no parameters is called a default constructor.

  30. // Java0808.java Stage #8 of the <Bank> class // Two methods are added that can read/write the attributes. // These are methods that make deposits to the checking and savings accounts. public class Java0808 { public static void main(String args[]) { System.out.println("\nJAVA0808.JAVA\n"); Bank tom = new Bank(1000.0,3000.0); Bank sue = new Bank(2000.0,2000.0); tom.checkingDeposit(1000.0); sue.savingsDeposit(2500.0); System.out.println("Tom's Checking Balance: " + tom.getChecking()); System.out.println("Tom's Savings Balance: " + tom.getSavings()); System.out.println(); System.out.println("Sue's Checking Balance: " + sue.getChecking()); System.out.println("Sue's Savings Balance: " + sue.getSavings()); System.out.println("\n\n"); } } class Bank { ////////// SET or MUTATOR "READ/WRITE" METHODS ////////// public void checkingDeposit(double amount) { checkingBal += amount; } public void savingsDeposit(double amount) { savingsBal += amount; } }

  31. // Java0809.java Stage #9 of the <Bank> class // Two more methods are added that can read/write the attributes. // These are methods that make withdrawals from the checking and savings accounts. // Note that the withdrawal methods have no protection against taking out more money than you have. public class Java0809 { public static void main(String args[]) { System.out.println("\nJAVA0809.JAVA\n"); Bank tom = new Bank(1000.0,3000.0); Bank sue = new Bank(2000.0,2000.0); tom.savingsWithdrawal(2500.0); sue.checkingWithdrawal(2500.0); System.out.println("Tom's Checking Balance: " + tom.getChecking()); System.out.println("Tom's Savings Balance: " + tom.getSavings()); System.out.println(); System.out.println("Sue's Checking Balance: " + sue.getChecking()); System.out.println("Sue's Savings Balance: " + sue.getSavings()); System.out.println("\n\n"); } } class Bank { public void checkingWithdrawal(double amount) { checkingBal -= amount; } public void savingsWithdrawal(double amount) { savingsBal -= amount; } }

  32. // Java0810.java Stage #10 of the <Bank> class // The withdrawal methods now protect against overdraft. Some extra printlns are added for clarification. public class Java0810 { public static void main(String args[]) { System.out.println("\nJAVA0809a.JAVA\n"); Bank tom = new Bank(1000.0,3000.0); Bank sue = new Bank(2000.0,2000.0); System.out.println("Tom asks the teller to withdraw $2500 from his savings account."); tom.savingsWithdrawal(2500.0); System.out.println("Sue asks the teller to withdraw $2500 from her checking account."); sue.checkingWithdrawal(2500.0); System.out.println("Tom's Checking Balance: " + tom.getChecking()); System.out.println("Tom's Savings Balance: " + tom.getSavings()); System.out.println(); System.out.println("Sue's Checking Balance: " + sue.getChecking()); System.out.println("Sue's Savings Balance: " + sue.getSavings()); System.out.println("\n\n"); } } class Bank { public void checkingWithdrawal(double amount) { if (amount > checkingBal) System.out.println("Insufficient Funds! Transaction Refused!\n"); else checkingBal -= amount; } public void savingsWithdrawal(double amount) { if (amount > savingsBal) System.out.println("Insufficient Funds! Transaction Refused!\n"); else savingsBal -= amount; } }

  33. // Java0811.java Stage #11 of the <Bank> class // The final stage of the <Bank> removes the class from the <Java0810.java> file // and creates a separate file, called Bank.java. public class Java0811 { public static void main(String args[]) { System.out.println("\nJAVA0811.JAVA\n"); Bank tom = new Bank(1000.0,3000.0); Bank sue = new Bank(2000.0,2000.0); tom.checkingWithdrawal(500.0); sue.savingsWithdrawal(800.0); System.out.println("Tom's Checking Balance: " + tom.getChecking()); System.out.println("Tom's Savings Balance: " + tom.getSavings()); System.out.println(); System.out.println("Sue's Checking Balance: " + sue.getChecking()); System.out.println("Sue's Savings Balance: " + sue.getSavings()); System.out.println("\n\n"); } }

  34. // Bank.java Stage #11 of the <Bank> class // The <Bank> is now placed in its own file, which is better program design. // You must now declare the class as "public". public class Bank { /////////// ATTRIBUTES ////////// private double checkingBal; private double savingsBal; ////////// CONSTRUCTOR METHODS ////////// public Bank() { checkingBal = 0.0; savingsBal = 0.0; } public Bank(double cBal, double sBal) { checkingBal = cBal; savingsBal = sBal; } ////////// GET "READ-ONLY" METHODS ////////// public double getChecking() { return checkingBal; } public double getSavings() { return savingsBal; } ////////// SET or MUTATOR "READ/WRITE" METHODS ////////// public void checkingDeposit(double amount) { checkingBal += amount; } public void savingsDeposit(double amount) { savingsBal += amount; } public void checkingWithdrawal(double amount) { if (amount > checkingBal) System.out.println("Insufficient Funds! Transaction Refused!\n"); else checkingBal -= amount; } public void savingsWithdrawal(double amount) { if (amount > savingsBal) System.out.println("Insufficient Funds! Transaction Refused!\n"); else savingsBal -= amount; } }

  35. Classes in Separate Files The previous program works because the Bank.java is located in the same folder as Java0811.java. It is very common to put each class in its own file. This is also the same reason why the Expo.java file is located in the folder as well. Way back in Chapter 2, you were told the name of the file must always match the name of the class. This is the reason why. If they did not match a file would not be able to find a class in another file. Java0811.java Bank.java Expo.java

  36. Section 8.5 Method Summary

  37. Class or Static Methods Class methods are sometimes called static methods because they have the keyword static in their heading. A class method is called with the class identifier, not with an object of the class. This is practical when there is no need to make multiple objects of a class. A good example is Java’s Math class.

  38. Class or Static Methods public class Demo { public static void main(String args[]) { Piggy.initData(); Piggy.showData(); Piggy.addData(1200); Piggy.showData(); } } class Piggy { public static double savings; public static void initData() { savings = 0; } public static void addData(double s) { savings += s; } public static void showData() { System.out.println("Savings: " + savings); } }

  39. Object or Non-Static Methods Object methods are sometimes called non-static methods because they do NOT have the keyword static in their heading. Object methods are meant for those situations where multiple objects of a class must be constructed. An object must be constructed first with the new operator, and then object methods are called by using the object identifier.

  40. Object or Non-Static Methods public class Demo { public static void main(String args[]) { Piggy tom = new Piggy(); tom.initData(); tom.showData(); tom.addData(1200); tom.showData(); } } class Piggy { private double savings; public void initData() { savings = 0; } public void addData(double s) { savings += s; } public void showData() { System.out.println("Savings: " + savings); } }

  41. Public Methods Essentially, public methods can be accessed anywhere. The majority of methods are public. public int getCards() { return cardsLeft; }

  42. Private or Helper Methods Occasionally, a method is created in a class that is never called outside of the class. In such a case, the method should be declared private. These private methods are sometimes called helper methods because they help and support the other methods of the class.

  43. Void Methods Void methods do NOT return a value and use the reserved word void to indicate that no value will be returned. public void showData() { System.out.println("Name: " + name); System.out.println("Savings: " + savings); }

  44. Return Methods Return methods are methods that return a value. Two features are necessary for a return method: First, you will see that the method heading indicates a data type, which is the type that the method returns. Second, you see a return statement at the end of the method body. public double getSavings() { return savings; }

  45. Default Constructor Methods A constructor is a special method that is automatically called during the instantiation of a new object. If no visible constructor is provided, Java will provide its own constructor, called a default constructor. Additionally, we also call a no-parameter constructor a default constructor. public CardDeck() { numDecks = 1; numPlayers = 1; cardsLeft = 52; shuffleCards(); }

  46. Overloaded Constructor Methods An overloaded constructor is a second, third or more, constructor that allows a new object to be instantiated according to some specifications that are passed by parameters. public CardDeck(int d, int p) { numDecks = d; numPlayers = p; cardsLeft = d * 52; shuffleCards(); }

  47. Accessing or Get Methods Methods that only access object data without altering the data are called accessing or get methods. Most accessing methods are return methods, which return object private data information. public int getDecks() { return numDecks; }

  48. Altering or Modifier or Mutator or Set Methods These are methods that not only access the private data of an object; they also alter the value of the data. public void savingsDeposit(double s) { savingsBal += s; }

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