Java C4. OOP Application pdf

1 Chapter 4. OOP Application ITSS Java Programming CAO Tuan-Dung, HUT 2 Inheritance  Mechanism to create new classes using existing classes  The existing class is called the parent class, or superclass , or base class  The derived class is called the child class or subclass  As the name implies, the child inherits characteristics of the parent  That is, the child class inherits the methods and data defined by the parent class 3 Benefit of Inheritance  Reusability  Once a behavior (method) is defined in a super class, that behavior is automatically inherited by all subclasses  Thus, you write a method only once and it can be used by all subclasses.  Once a set of properties (fields) are defined in a super class, the same set of properties are inherited by all subclasses  A class and its children share common set of properties  A subclass only needs to implement the differences between itself and the parent. 4 Inheritance Superclass Account Superclass Account Sub-class IntegratedAccount Basic function of Account + Class that defines original behavior Class that defines basic function of Account All the behaviors of superclass(attribute, operation, relation) are inherited to the sub-class 5 Definition of sub-class  To derive a child class, we use the extends keyword.  Syntax: [Modifier] class Sub-class_name extends SuperClass_name{ Definition of member variable to add Method definition to add or redefine } // Account class (superclass) class Account { String name; //Account name int balance; //Balance void display(){… } // Display } // Integrated account class (sub-class) class IntegratedAccount extends Account { int limitOverdraft; //Borrowing amount limit int overdraft; //Borrowing amount void loan(int money){…} //Borrowing() void display(){… } // Display } IntegratedAccount obj= new IntegratedAccount(); 6 Another example public class Person { protected String name; protected String address; /** * Default constructor */ public Person(){ System.out.println(“Inside Person:Constructor”); name = ""; address = ""; } . . . . } 7 Object of sub-class name balance display(){…} superclass part object of sub-class limitOverdraft overdraft display2(){…} loan(){…} In the object of the sub- class, there are the member variable and the method that were defined by the superclass, and the member variable and the method that were added by the sub-class. 8 Example: Inheritance.java // Account class class Account { // Member variable private String name; // Account name private int balance; // Balance // Value setting Method public void setData(String pName, int pInitialBalance) { name = pName; balance = pInitialBalance; } // Value setting Method public void display() { System.out.print("Account name ： " + name); System.out.println(“\tBalance ： " + balance + “VND"); } } // Integrated account class class IntegratedAccount extends Account { // Additional member variable private int limitOverdraft; // Borrowing amount limit private int overdraft; // Borrowing amount // Additional method // // Setting of borrowing amount limit Method public void setLimitOverdraft(int pLimitOverdraft) { limitOverdraft = pLimitOverdraft; overdraft = 0; } public void loan(int pOverdraft) { if((overdraft+pOverdraft) <= limitOverdraft) { overdraft += pOverdraft; } else { System.out.println(“Total of borrowing exceeds borrowing amount limit "); } } 9 Inheritance.java // Display of value 2 Method public void display2() { System.out.println(“\t\t Borrowing amount limit ： "+ limitOverdraft + “VND"); System.out.println(“\t\t Borrowing amount ： " + overdraft + “VND"); } } // Application class Exercise of inheritance class Inheritance { public static void main(String args[]) { // Generation of sub-class’s object IntegratedAccount obj = new IntegratedAccount(); // Method call of superclass (Message transmission) obj.setData(“Duc Binh", 100000); obj.display(); // Method call of sub-class (Message transmission) obj.setLimitOverdraft(500000); obj.loan(200000); obj.display2(); } } 10 Override  Redefine by the subclass the method is defined by the super class.  A child class can override the definition of an inherited method in favor of its own  The new method must have the same signature as the parent's method, but can have a different body  The type of the object executing the method determines which version of the method is invoked [...]... { super.display(); // Call of superclass method System.out.println(“Borrowing amount limit" + limitOverdraft + "Yen"); System.out.println(" Borrowing amount" + overdraft + "Yen"); } } 21 ThisSuper .java // Application class ThisSuper class ThisSuper { public static void main(String args[]) { // For constructor without argument, call constructor with argument g, g Account obj = new Account(); obj.display();... void loan(int pOverdraft) { if((overdraft+pOverdraft) . 1 Chapter 4. OOP Application ITSS Java Programming CAO Tuan-Dung, HUT 2 Inheritance  Mechanism to create new classes. the member variable and the method that were added by the sub-class. 8 Example: Inheritance .java // Account class class Account { // Member variable private String name; // Account name private. System.out.println(“Total of borrowing exceeds borrowing amount limit "); } } 9 Inheritance .java // Display of value 2 Method public void display2() { System.out.println(“ Borrowing amount