Question

Introduction

In this lab, you will be working with three classes: Person, Student, and Roster.

Person and Student represent individuals with a first and last name as String class variables, and Student has an additional int class variable that represents a ID number.

The Roster class represents a group of people that are objects of either the Person or Student class. It contains an ArrayList.

The Person class has been completed for you with class variables, a constructor, and a toString() method. You will be responsible for finishing the Roster class, and writing the Student class from scratch.

Step 1: Student Class

Define the Student class to inherit from the Person class.

Declare an int class variable to represent the ID number.

Write the constructor to initialize all class variables.

Also, define the toString() method to resemble the toString() method from the Person class, except with the ID following the name.

The format should resemble: Student: FirstName LastName IDnumber

Step 2: Roster.initializeListFromFile()

Now, complete the unfinished initializeListFromFile() in the Roster class. This method takes a filename as a parameter and fills the ArrayList of objects of type Person or Student.

Each line in the file to read from represents a single object with the following possible formats: For a Student object: firstName lastName idNumber

For a Person object: firstName lastName

We recommend using the String method .split() which returns an array of strings, to parse the line.

Your method should loop through every line in the file, and add a new Person or Student object to the people ArrayList by calling the appropriate constructor with the appropriate arguments.

Test Your Methods

As usual, you will also be able to test your code within the Main class. You may run your program in Develop mode as many times as you would like, but you may only submit your program once.

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Student.java CODE:

// Step 1: Student Class

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Roster.java CODE:

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class Roster {

    ArrayList<Person> people;

    public Roster(String filename) {
        people = new ArrayList<Person>();
        initializeListFromFile(filename);
    }

    public void initializeListFromFile(String filename) {
        try {
            // Step 2
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

    public static void main(String [] args) {
        Roster r = new Roster("test");
        System.out.println(r.people);
    }

}

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Person.java CODE:

public class Person {
    String firstName;
    String lastName;

    public Person(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public String toString() {
        return "Person: " + firstName + " " + lastName;
    }



}

Answer 1

Roster.java

//Roster.java

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class Roster {

    ArrayList<Person> people;
    ArrayList<Student> students;


    public Roster(String filename ) {
        people = new ArrayList<Person>();
        students = new ArrayList<Student>();
        initializeListFromFile(filename);
    }

    public void initializeListFromFile(String filename) {
        try {
            Scanner scnr = new Scanner(new File(filename));
            while (scnr.hasNextLine()) 
            {
                String tmp = scnr.nextLine();
                String[] li = tmp.split(" ");
                if(li.length == 3)
                {
                    // Student Object
                    students.add(new Student(li[0], li[1], Integer.parseInt(li[2])));
                
                }
                else if(li.length == 2)
                {
                    // Person Object
                    people.add(new Person(li[0],li[1]));
                }
                else
                {
                    System.out.println("Invalid entry in file: " + filename);
                    System.exit(1);
                }
            }
            scnr.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

    public static void main(String [] args) {
        Roster r = new Roster("test.txt");
        System.out.println(r.people);
        System.out.println(r.students);
    }

}

Student.java

// Student.java


public class Student extends Person {
    int id;

    public Student(String firstName, String lastName, int id) {
        super(firstName, lastName);
        this.id = id;
    }

    public String toString() {
        return "Student: " + firstName + " " + lastName + " " + id;
    }



}

Person.java

// Person.java

public class Person {
    String firstName;
    String lastName;

    public Person(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public String toString() {
        return "Person: " + firstName + " " + lastName;
    }



}

Test input file , name : test.txt

Alexander Supertramp
Alaska Green 12
Adam Abraham 2
Camila Black 19
Alice Thomas
Christopher Nolan
David Fincher 123
James Hall 
John Franklin 122

Keeping Roster.java , Student.java , Person.java in the same folder ( also copy test.txt to to the same directory for verification)

Compile :

javac Roster.java

run :

java Roster

Output Sample :

[Person: Alexander Supertramp, Person: Alice Thomas, Person: Christopher Nolan, Person: James Hall] [Student: Alaska Green 12, student: Adam Abraham 2, Student: Camila Black 19, student: David Fincher 123, Student: John Franklin 122] lachadow workencos

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