Question

This question demonstrates the use of inheritance and polymorphism.
Design a Ship class that has the following members:
• A field for the name of the ship (a string).
• A field for the year that the ship was built (a string).
• A constructor and appropriate accessors and mutators.
• A toString method that overrides the toString method in the Object class. The Ship class
toString method should display the ship’s name and the year it was built.
Design a CruiseShip class that extends the Ship class. The CruiseShip class should have the following members:
• A field for the maximum number of passengers (an int).
• A constructor and appropriate accessors and mutators.
• A toString method that overrides the toString method in the base class. The CruiseShip class’s
toString method should display only the ship’s name and the maximum number of passengers.
Design a CargoShip class that extends the Ship class. The CargoShip class should have the following members:
• A field for the cargo capacity in tonnage (an int).
• A constructor and appropriate accessors and mutators.
• A toString method that overrides the toString method in the base class. The CargoShip class’s
toString method should display only the ship’s name and the ship’s cargo capacity.
Demonstrate the classes in a program that has a Ship array. Assign various Ship, CruiseShip, and CargoShip objects to the array elements. The program should then step through the array and print each object.

Answer 1

Short Summary:

• Provided the source code and sample output as per the requirements.

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Source Code:

Ship.java:
public class Ship {
   String name;
   String year;
  
   public Ship(){
       name = "";
       year = "";
   }
  
   // constructor parameterized
   public Ship(String name, String year) {
       this.name = name;
       this.year = year;
   }
  
  

   /**
   * @return the name
   */
   public String getName() {
       return name;
   }

   /**
   * @param name the name to set
   */
   public void setName(String name) {
       this.name = name;
   }

   /**
   * @return the year
   */
   public String getYear() {
       return year;
   }

   /**
   * @param year the year to set
   */
   public void setYear(String year) {
       this.year = year;
   }

   public String toString() {
       return this.name + " " + this.year;
   }
  
}

CruiseShip.java:
class CruiseShip extends Ship {
   // attribute of CruiseShip
   private int maximumPassenger;

   // Constructor parameters
   public CruiseShip(String name, String year, int capacity) {
       super(name, year);
       maximumPassenger = capacity;
   }

   // accessor and mutator
   public void setPassengerCapacity(int capacity) {
       maximumPassenger = capacity;
   }

   public int getPassengerCapacity() {
       return maximumPassenger;
   }

   //
   @Override
   public String toString() {
       String result = "";
       result = "Cruise Ship \n";
       result = result + "Name: " + getName() + "\n";
       result = result + "Passenger Capacity: " + getPassengerCapacity() + " persons\n";
       return result;
   }
}

CargoShip.java:

//subclass CargoShip from superclass Ship
public class CargoShip extends Ship {
   // private member variable of CargoShip class
   private int tonnage;

   // Constructor parameters
   public CargoShip(String name, String year, int weight) {
       super(name, year);
       this.tonnage = weight;
   }

   // accessor and mutator
   public void setTonnage(int weight) {
       tonnage = weight;
   }

   public int getTonnage() {
       return tonnage;
   }

   // The toString() method overridden by the subclass
   @Override
   public String toString() {
       String result = "";
       result = "Cargo Ship \n";
       result = result + "Name: " + getName() + "\n";
       result = result + "Cargo Capacity: " + getTonnage() + " tons\n";
       return result;
   }
}

main.cpp:

public class DemoMain {
  
   // Driver method to create objects of all three ships and print their details
   public static void main(String[] args) {
       // Create an array of type Ship, to hold Ship objects
       Ship ShipArray[] = new Ship[3];

       // Create an object of super class Ship
       Ship ship1 = new Ship("Ship Element", "1978");

       // Create an object of subclass CruiseShip
       Ship ship2 = new CruiseShip("Cruise Ship Element", "1978", 5000);
      
       // Create an object of subclass CargoShip
       Ship ship3 = new CargoShip("CargoShip Element", "1978", 20000);

       // Store all three objects in the array
       ShipArray[0] = ship1;
       ShipArray[1] = ship2;
       ShipArray[2] = ship3;

       // Iterate through Loop through the array to print all ships
       for (int index = 0; index < ShipArray.length; index++) {
           System.out.println(ShipArray[index]);
           System.out.println();
       }
   }
}

Sample Run:

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