Class Inheritance

1
Class Inheritance

• Implement Base Classes.
• Implement Derived Classes.
• Call Base Class Methods .
• Override Base Class Methods .
• Initialize Base Classes from Derived Classes.

2
Inheritance (Textbook chapter 10)

• A primary object-oriented programming concept
• Main advantage code reuse
• Higher-level Base classes group common properties
  and operations
• Lower-level Derived classes define more specific
  details

3
Define Base and Derived classes

• using Systempublic class MyBaseClass   
  public MyBaseClass()           
  Console.WriteLine(" MyBaseClass
  Constructor.")        public void
  print()            Console.WriteLine("I'm a
  Base Class.")    public class
  MyDerivedClass MyBaseClass     public
  MyDerivedClass () base()           
  Console.WriteLine(MyDerivedClass
  Constructor.")        public static void
  Main()            MyDerivedClass derived new
  MyDerivedClass ()        derived.print()   
  

• Colon specifies inheritance (from a class or
  interface).
• Derived class inherited all public members in the
  base class.
• You can treat MyDerivedClass as MyBaseClass.
• During instantiation, base class constructor is
  called before the constructor of the derived class

Output MyBaseClass Constructor.MyDDerivedClass
Constructor.I'm a Base Class.
4
Initialize Base Class in Derived Class

• class BankAccount
• private double balance
  
• public BankAccount(double initialAmount)
• balance initialAmount
• //.(other BankAccount members)
• / Creates a constructor for the derived class
  which calls the
• base class constructor.
• /
• public class SimpleSavings2 BankAccount
• public SimpleSavings2(double amount)
  base(amount)

indicates a call to a base class class
constructor. Keyword base represent the base
class.
5
Override Base class methods

• using Systempublic class MyBaseClass   
  public MyBaseClass()           
  Console.WriteLine(" MyBaseClass
  Constructor.")        public virtual void
  print()            Console.WriteLine("I'm a
  Base Class.")    public class
  MyDerivedClass MyBaseClass     public
  MyDerivedClass ()           
  Console.WriteLine(MyDerivedClass
  Constructor.")        public static void
  Main()            MyDerivedClass derived new
  MyDerivedClass ()        derived.print()   
  

• A derived class automatically inherits the public
  methods of its base class,
• but it may choose to override some of them to
  implement its own specific operations.
• (Project 8 10.9)

1
2
public override void print()
Console.WriteLine(Im a Derived class)
Output MyBaseClass Constructor.MyDDerivedClass
Constructor.I'm a Derived Class.
6
The Account Hierarchy
BankAccount balance GetBalance Deposit Withdraw
ReadAccount
Base class
Derived class
Derived class

• CheckingAccount overrides Withdraw method
  inherited from BankAccount
• In exercise 10.0, you need to add a ReadAccount
  method to BankAccount and override it in
  SavingsAccount and CheckingAccount.

7
Testing code for Project 8

• Testing code
• http//www.cs.uiowa.edu/zhihwang/ta016/TestAccoun
  ts.cs
• For your reference
• http//www.cs.uiowa.edu/zhihwang/ta016/BankAccoun
  t.cs
• http//www.cs.uiowa.edu/zhihwang/ta016/SavingsAcc
  ount.cs
• http//www.cs.uiowa.edu/zhihwang/ta016/CheckingAc
  count.cs