I. Inheritance

• Definition:
• The concept of classes automatically containing the variables and methods defined in their supertypes.    
• Keyword: super, abstract, extends
• super - the keyword used to call methods of the superclass. i.e. super.speak( )
• abstract - the keyword used to create an abstract class or a class that has behaviors that are only partially implemented
• allows the subclasses to be filled with the details or situation dependent behaviors
• i.e. abstract class abstractClass {...}
        class subClass extends abstractClass {...}
  
• extends - the keyword used to create a subclass of a superclass. i.e. class subClass extends superClass
  
• Purpose/Benefits:
• Subclasses have specialized behaviors for that particular class but also show common elements of the super class.
• Allows grouping of classes.
  
• Increases code reusability.
• Keys
• Subclasses can mold their superclasses.
• Subclasses can add variables and methods to the ones they inherit from the superclass.
• Subclasses can override methods in the super classes to specialize them.
• You can not extend more than one superclass for any given class.
• You can have multiple layers in an inherited hierarchy.
• Methods and variables are inherited through the layers.
• The super class of all classes is the Object class.
• It provides the behaviors of all objects running in the JVM.
• like toString( ), equals( ), and clone( )
  
• i.e. all objects (therefore all classes) have the toString( ) method which outputs the hashcode of the object. This is inherited from the Object super class.

II. Interfaces

• Definition:
• A group or collection of method definitions and constant values.
• Keyword: implements - allows a class to realize the interface
  
• Purpose/Benefits:
  
• Capturing similarities among unrelated classes without artificially forcing a class relationship.
• Declaring methods that one or more classes are expected to implement.
• Revealing an object's programming interface without revealing its class.
• Keys
• When a class realizes an interface, it agrees to follow the interfaces behavior.
• Therefore, it must have all of the methods in the interface in the realizing class.
• Holds a constant protocol of method definitions
• A class can implement as many interfaces as you want.

III. Multiple Choice

1. Which of the following would best serve as the interface to the other items listed?
   

   a. Washing Machine
   b. Refridgerator
   c. MicrowaveOven
   d. Appliance
   e. Dryer
   

   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
2. Given the following class definition:
   public class Vehicle
   {
          public void drive(double miles)
          {
             ...
          }
   }
   Why won't this subclass compile?
   public class Car extends Vehicle
   {
         private void drive(double miles)
         {
           ...
         }
   }
   A) It will compile.
   B) The drive method of the Car class can not have a different return type.
   C) A method can never be declared private.
   D) Car can not have a method with the same name as one in its superclass.
   E) A method must have a different parameter name.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
3. 
   Given the following Java code:
   
<><>
interface Animal {
  public void speak();
}

class Canine implements Animal {
  public void speak() {
    System.out.print("Canine:");
  }
  public static void main(String[] args) {
    Animal a = null;
    Canine c = null;
    // What could go here?
  }
}A) c = a;
B) a = c;
C) c= new Canine();
D) B and C
E) A and C


















4. Given that the Employee class extends Person class and this segment of code:
   Employee boss = new Employee();
   Person mom = new Person();
   Object anObject;
   Person tom;
   Which of the following assignments are valid?
   
   A) boss = mom;
   B) anObject = boss;
   C) mom = boss;
   D) B and C
   E) A, B, and C
   
   
   
   
   
   
   
   
   
   
   
   
   
   
5. Given the following code segments:
   public class Country implements Locatable
   {
       ....
   }
   public class Tester
   {
      ....
      Country norway = new Country();
      statement2
   }
   Which of the following statemens would be valid as statement2?
   
   A) Locatable where = norway;
   B) Locatable where = new Locatable();
   C) Locatable where = Country();
   D) Locatable where = new York();
   E) Country where = new Locatable();
   

Free Response Question

An airport needs a program to document the different flights leaving
Given the following class:
     BankAccount
a.) Write a CheckingAccount class that is a subclass of BankAccount that charges transaction fees per transactions, which is entered by the user. You should modify the methods as necessary, add any necessary local variables, and add a deductFees( ) method that deducts the fees for the number of transactions and then resets the transaction count.

b.) Write a SavingsAccount class that is a subclass of BankAccount that earns interest at a fixed rate and has an addInterest( ) method allow the account to earn interest in the account balance. You may use any of the methods added or modified in part A. Assume that the deductFees( ) method works as it should regardless of you answer in part A.


















Answers:
1. D
2. B
3. D
4. D
5. A

FRQ Answers
A.) CheckingAccount
B.) SavingsAccount