Question

Assignment (to be done in Java):

Change the Person class to an abstract class.

Person Class:

public class Person extends Passenger{
private int numOffspring;

public Person() {
   this.numOffspring = 0;
}

public Person (int numOffspring) {
   this.numOffspring = numOffspring;
}

public Person(String name, int birthYear, double weight, double height, char gender, int numCarryOn, int numOffspring)
{
   super(name, birthYear, weight, height, gender, numCarryOn);
  
   if(numOffspring < 0) {
       this.numOffspring = 0;
   }
   this.numOffspring = numOffspring;
}

public int getNumOffspring() {
   return numOffspring;
   }
public void setNumOffspring(int numOffspring) {
   if(numOffspring < 0)
       this.numOffspring = 0;
   this.numOffspring = numOffspring;
}

@Override
public void printDetails() {
   System.out.printf("Person: Number of Offspring: %4d\n", getNumOffspring());
  
}

@Override
public boolean equals(Object p)
{
   if (p instanceof Person)
   {
   Person person = (Person) p;
   return (super.equals(p) && getNumOffspring() == person.getNumOffspring());
   }
   return false;
   }

}

Passenger Class (just in case):

import java.util.Calendar;
import java.util.Date;

public class Passenger
{
private String name;
private int birthYear;
private double weight;
private double height;
private char gender;
private int numCarryOn;
  

public Passenger()
{
this.name="";
this.birthYear=1900;
this.weight=0.0;
this.gender='u';
this.numCarryOn=0;
}   

public Passenger(String name,int birthYear,double weight, double height, char gender,int numCarryOn)
{
this.name=name;
this.birthYear=birthYear;
this.weight=weight;
this.height=height;
this.gender=gender;
this.numCarryOn=numCarryOn;
}   
  
public double calculateBMI ()
{
return ((weight * 703) / (height * height));
}
  

public int calculateAge(int currentYear)
{

if(currentYear < birthYear)
return -1;
else
return currentYear-this.birthYear;
}

public void gainWeight()
{
this.weight+=1;
}

public void gainWeight(double gain)
{
this.weight+=gain;
}

public int getBirthYear()
{
return this.birthYear;
}

public char getGender()
{
return this.gender;
}

public String getName()
{
return this.name;
}

public double getWeight()
{
return this.weight;
}

public double getHeight()
{
return this.height;
}

public int getNumCarryOn()
{
return this.numCarryOn;
}

public boolean isFemale()
{
if(this.gender=='f' || this.gender=='F')
return true;
else
return false;
}

public boolean isMale()
{
if(this.gender=='m' || this.gender=='M')
return true;
else
return false;
}

public void loseWeight()
{
this.weight-=1;
if(this.weight < 0) {
System.out.println("Weight can not drop below zero");
this.weight+=1;
}
}

public void loseWeight(double loss)
{
this.weight-=loss;
if(this.weight < 0) {
System.out.println("Weight can not drop below zero");
this.weight+=loss;
}
}
  
@Override
public String toString ()
{
String s = String.format ("Name: %20s | Year of Birth: %4d | Weight: %10.2f | Height: %10.2f | Gender: %c | NumCarryOn: %2d\n",
this.name,this.birthYear,this.weight, this.height, this.gender,this.numCarryOn);
return s;
}
  
@Override
public boolean equals (Object o)
{
if (o == this) return true;
  
Passenger p = (Passenger) o;
if ( (p.birthYear == this.birthYear) && (p.gender == this.gender) && (p.name == this.name) &&
(Math.abs(p.weight - this.weight) < 0.5) && (Math.abs(p.height - this.height) < 0.5) )
return true;
else
return false;
}
  

public void printDetails()
{
System.out.printf("Name: %20s | Year of Birth: %4d | Weight: %10.2f | Height: %10.2f | Gender: %c |"
+ " NumCarryOn: %2d\n",this.name,this.birthYear,this.weight, this.height, this.gender,this.numCarryOn);
}

public void setGender(char gender)
{
if(gender != 'm' || gender != 'f' ||(gender != 'M' || gender != 'F'))
this.gender='u';
else
this.gender = gender;
}

public void setName(String name)
{
this.name=name;
}

public void setBirthYear(int birthYear)
{
this.birthYear=birthYear;
}

public void setHeight(double height)
{
if(height < 0)
this.height = -1;
else
this.height=height;
}

public void setWeight(double weight)
{
if(this.weight < 0)
weight = -1;
else
this.weight=weight;
}

public void setNumCarryOn(int numCarryOn)
{
if(numCarryOn < 0)
numCarryOn = 0;
else if (numCarryOn > 2)
this.numCarryOn = 2;
else
this.numCarryOn=numCarryOn;
}
}

Answer 1

You only need to add abstract keyword in front of Person class and then create some other class (in my code Individual) which inherits from it. See the code below:

// abstract keyword addded
abstract class Person extends Passenger{
        private int numOffspring;
        public Person() {
           this.numOffspring = 0;
        }

        public Person (int numOffspring) {
           this.numOffspring = numOffspring;
        }

        public Person(String name, int birthYear, double weight, double height, char gender, int numCarryOn, int numOffspring)
        {
           super(name, birthYear, weight, height, gender, numCarryOn);
          
           if(numOffspring < 0) {
               this.numOffspring = 0;
           }
           this.numOffspring = numOffspring;
        }
        
        public int getNumOffspring() {
           return numOffspring;
        }
        public void setNumOffspring(int numOffspring) {
           if(numOffspring < 0)
               this.numOffspring = 0;
           this.numOffspring = numOffspring;
        }

        @Override
        public void printDetails() {
           System.out.printf("Person: Number of Offspring: %4d\n", getNumOffspring());
          
        }

        @Override
        public boolean equals(Object p)
        {
           if (p instanceof Person)
           {
                   Person person = (Person) p;
                   return (super.equals(p) && getNumOffspring() == person.getNumOffspring());
           }
           return false;
        }
        
        
}

// this is the new class which inherits from abstract class Person
class Individual extends Person {

}

As we made the Person class as abstract, now it can't be instantiated. To make that possible in a virtual fashion, we make another class which inherits from it and hence can access all its public attributes & public methods.

From the code, you can see I've created a class Individual which inherits from abstract class Person.

This class can be instantiated & can be used to access Person's methods as shown below:

// this is just the main function
public static void main(String[] args) {
                
        Individual i = new Individual();
        i.setNumOffspring(2);
        i.printDetails();
}

Sample Output for this above code snippet:

<terminated > AbstractClass [Java Application] D:\Installed Softwares\java-11.0.8\bin\javaw.exe (Oct 6, 2020, 2:43:09 PM) Person: Number of Offspring: 2

Hope this solves your concern. For any further doubt, feel free to reach back, I'd be happy to help! :)

If it helped, please consider giving an upvote, I'd appreciate that! :)

Cheers & Have a great learning ahead!