Question

FOR JAVA:

Summary: Create a program that adds students to the class list (see below).

The solution should be named Roster402_v2.java. Allow the user to control the number of students added to the roster. Ask if the user would like to see their new roster to confirm additions. If yes, then display contents of the file, if no, end the program.

-------------------------------------------------------------------------------------

List of student names and IDs for class (this will be your separate text file):

• Jones, Jim,45
• Hicks, Josh,56
• Perry, Andy,82
• Rush, Ashely,19
• Salenga, Aaron,55
• Matos, Pamela,22
• Jeffries, Rick,87
• Bush, Fred,40
• Ashford, Kate,52
• Naamah, Ester,68
• Lachlan, Bae,35
• Eachann, Steven,41
• Ubon, Peter,16
• Bacon, Gabe,59
• Rockson, Kurt,77

----------------------------------------------------------------------------

Student.java

public class Student {
private String lastName, firstName;
private int ID;
  
public Student()
{
this.lastName = this.firstName = "";
this.ID = 0;
}

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

public String getLastName() {
return lastName;
}

public String getFirstName() {
return firstName;
}

public int getID() {
return ID;
}
  
@Override
public String toString()
{
return(this.ID + " - " + this.firstName + " " + this.lastName);
}
}

Roster.java

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.Scanner;

public class Roster {
private LinkedList<Student> students;
  
public Roster()
{
this.students = new LinkedList<>();
}
  
public void readStudents(String fileName)
{
Scanner fileReader;
try
{
fileReader = new Scanner(new File(fileName));
while(fileReader.hasNextLine())
{
String[] data = fileReader.nextLine().trim().split(",");
String lastName = data[0];
String firstName = data[1];
int ID = Integer.parseInt(data[2]);
  
this.students.add(new Student(lastName, firstName, ID));
}
fileReader.close();
}catch(FileNotFoundException fnfe){
System.out.println("Couldn't find " + fileName);
System.exit(1);
}
}
  
public void sortByLastName()
{
Collections.sort(this.students, new CompareByLastName());
}
  
public void sortByID()
{
Collections.sort(this.students, new CompareByID());
}
  
public void displayList()
{
for(Student student : this.students)
{
System.out.println(student);
}
}
  
private class CompareByLastName implements Comparator<Student>
{
@Override
public int compare(Student o1, Student o2) {
if(o1.getLastName().compareTo(o2.getLastName()) < 0)
return -1;
else if(o1.getLastName().compareTo(o2.getLastName()) == 0)
return 0;
else
return 1;
}
}
  
class CompareByID implements Comparator<Student>
{
@Override
public int compare(Student o1, Student o2) {
if(o1.getID() < o2.getID())
return -1;
else if(o1.getID() == o2.getID())
return 0;
else
return 1;
}
}
}

RosterDemo.java (Main class)

import java.util.Scanner;

public class RosterDemo {
  
private static final String FILENAME = "students.txt";
  
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
Roster roster = new Roster();
roster.readStudents(FILENAME);
  
System.out.println("ORIGINAL LIST OF ALL STUDENTS:\n------------------------------");
roster.displayList();
System.out.println();
  
int choice;
do
{
printMenu();
choice = Integer.parseInt(sc.nextLine().trim());
switch(choice)
{
case 1:
{
System.out.println("\nSorting students based on their last names:");
roster.sortByLastName();
roster.displayList();
System.out.println();
break;
}
  
case 2:
{
System.out.println("\nSorting students based on their IDs:");
roster.sortByID();
roster.displayList();
System.out.println();
break;
}
  
case 3:
{
System.out.println("\nThank you..Goodbye!\n");
System.exit(0);
}
  
default:
System.out.println("\nInvalid selection!\n");
}
}while(choice != 3);
}
  
private static void printMenu()
{
System.out.print("1. Sort by last name\n"
+ "2. Sort by ID\n"
+ "3. Exit\n"
+ "Your selection >> ");
}
}

Answer 1

In this program i have added one more option in the menu as Add Student

which will ask you to enter first name,last name and id. After that it will update the student.txt file.

Then it will ask you whether you want to see new roster or not according to your response it will show.

class CompareByID implements Comparator<Student> {

@Override
public int compare(Student o1, Student o2) {
if (o1.getID() < o2.getID()) {
return -1;
} else if (o1.getID() == o2.getID()) {
return 0;
} else {
return 1;
}
}
}

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.Scanner;

public class Roster {

private LinkedList<Student> students;

public Roster() {
this.students = new LinkedList<>();
}

public void readStudents(String fileName) {
Scanner fileReader;
try {
fileReader = new Scanner(new File("C:\\Users\\i334075\\Documents\\NetBeansProjects\\JavaApplication1\\src\\javaapplication1\\students.txt"));
while (fileReader.hasNextLine()) {
String[] data = fileReader.nextLine().trim().split(",");
String lastName = data[0];
String firstName = data[1];
int ID = Integer.parseInt(data[2]);

this.students.add(new Student(lastName, firstName, ID));
}
fileReader.close();
} catch (FileNotFoundException fnfe) {
System.out.println("Couldn't find " + fileName);
System.exit(1);
}
}
// This function write the detail at the end of the file.
public void writeToStudents(String entry) throws IOException {
String fileName = "students.txt";
try {   
  
PrintWriter writer = new PrintWriter (new FileWriter(fileName, true));
writer.append(' ');
writer.append(entry+"\n");
writer.close();
} catch (FileNotFoundException fnfe) {
System.out.println("Couldn't find " + fileName);
System.exit(1);
}
}

public void sortByLastName() {
Collections.sort(this.students, new CompareByLastName());
}

public void sortByID() {
Collections.sort(this.students, new CompareByID());
}

public void displayList() {
for (Student student : this.students) {
System.out.println(student);
}
}

private class CompareByLastName implements Comparator<Student> {

@Override
public int compare(Student o1, Student o2) {
if (o1.getLastName().compareTo(o2.getLastName()) < 0) {
return -1;
} else if (o1.getLastName().compareTo(o2.getLastName()) == 0) {
return 0;
} else {
return 1;
}
}
}
}

import java.io.IOException;
import java.util.Scanner;

public class RosterDemo {

private static final String FILENAME = "students.txt";

public static void main(String[] args) throws IOException {
Scanner sc = new Scanner(System.in);
Roster roster = new Roster();
roster.readStudents(FILENAME);

System.out.println("ORIGINAL LIST OF ALL STUDENTS:\n------------------------------");
roster.displayList();
System.out.println();

int choice;
String firstName;
String lastName;
int userInput;
int id;
do {
printMenu();
choice = Integer.parseInt(sc.nextLine().trim());
switch (choice) {
case 1: {
System.out.println("\nSorting students based on their last names:");
roster.sortByLastName();
roster.displayList();
System.out.println();
break;
}

case 2: {
System.out.println("\nSorting students based on their IDs:");
roster.sortByID();
roster.displayList();
System.out.println();
break;
}
case 3: {
System.out.println("\nAdd student:");
System.out.println("\nEnter first name:");
firstName = sc.nextLine().trim();
System.out.println("\nEnter last name:");
lastName = sc.nextLine().trim();
System.out.println("\nEnter ID:");
id = Integer.parseInt(sc.nextLine().trim());
roster.writeToStudents(firstName + "," + lastName + "," + id);
System.out.println("\nDo you want to see your new roster ?:");
System.out.println("\n1. YES");
System.out.println("\n2. NO");
userInput = Integer.parseInt(sc.nextLine().trim());
if (userInput == 1) {
roster.readStudents(FILENAME);
roster.displayList();
}else{
System.exit(0);
}
break;
}

case 4: {
System.out.println("\nThank you..Goodbye!\n");
System.exit(0);
}

default:
System.out.println("\nInvalid selection!\n");
}
} while (choice != 3);
}

private static void printMenu() {
System.out.print("1. Sort by last name\n"
+ "2. Sort by ID\n"
+ "3. Add Student\n"
+ "4. Exit\n"
+ "Your selection >> ");
}
}

public class Student {

private String lastName, firstName;
private int ID;

public Student() {
this.lastName = this.firstName = "";
this.ID = 0;
}

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

public String getLastName() {
return lastName;
}

public String getFirstName() {
return firstName;
}

public int getID() {
return ID;
}

@Override
public String toString() {
return (this.ID + " - " + this.firstName + " " + this.lastName);
}
}