Application error using vector java.lang.Nullpointerexception

Question

Good morning.

I’m trying to perform a proposed exercise in a Java course that I’m doing but I’m not getting it. This is a simple program that simulates the reservation of a hostel using vectors.

I need that, after selecting the amount of rooms that will be reserved, the program request the customer’s name(Student).

However when I run the program and type the client name it appears the following error:

Exception in thread "main" java.lang.NullPointerException
at application.Program.main(Program.java:25)

I believe the error is inside the block for in the stretch s[i].setName(n); class Main

But I couldn’t fix it.

Below are the codes(classes Program, Hostel and Student I’m using in this Java project:

package application;

import java.util.Scanner;

import entities.Hostel;
import entities.Student;

public class Program {

    public static void main(String[] args) {
        Hostel h[];
        h = new Hostel[10];

        Scanner sc = new Scanner(System.in);

        System.out.print("How many rooms will be rented?: ");
        int room = sc.nextInt();
        Student[] s = new Student[room];
        sc.nextLine();

        for(int i =0; i<s.length; i++) {
            System.out.println("RENT #"+i);
            System.out.print("Name :");
            String n = sc.nextLine();
            s[i].setName(n);
        }
        sc.close();
    }
}

package entities;

public class Hostel {
    private int room;
    private char situation;


    public int getRoom() {
        return room;
    }
    public void setRoom(int room) {
        this.room = room;
    }
    public char getSituation() {
        return situation;
    }
    public void setSituation(char situation) {
        this.situation = situation;
    }


}

package entities;

public class Student {
    private String name;
    private String email;

    public Student(String name, String email) {
        this.name = name;
        this.email = email;
    }

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }

}

Answer 1

Check the null pointer on line 25. That’s it.

You need to instantiate the variable s, guy:

s[i] = new Student();

Remember that in your class Student there is no constructor without the parameters, it is important to create there.

Example:

public Student(){
}

---

public static void main(String[] args) {
    Hostel h[];
    h = new Hostel[10];

    Scanner sc = new Scanner(System.in);

    System.out.print("How many rooms will be rented?: ");
    int room = sc.nextInt();
    Student[] s = new Student[room];
    sc.nextLine();

    for(int i =0; i<s.length; i++) {
        System.out.println("RENT #"+i);
        System.out.print("Name :");
        String n = sc.nextLine();
        s[i] = new Student();
        s[i].setName(n);
    }
    sc.close();
}