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I am trying to access an object from an array of objects in a simple program. For hours , I have been scratching my head.

The moment I try to call the object from the array of objects using its INDEX VALUE, the output is error.

Problem: I am trying to take details from three students and store them in objects . Student s[]=new Student[2]; but when I am trying to access s[i].getName()- there is a an error.It says s[i] is null.You can see the output as shown below.

The details for three students are taken in a do-while loop until q!=1 as condition.

Here is my model class:

public class Student {

    private String name;
    private String id;
    private int phoneNumber;



    public String getName() {
        return name;
    }

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

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public int getPhoneNumber() {
        return phoneNumber;
    }

    public void setPhoneNumber(int phoneNumber) {
        this.phoneNumber = phoneNumber;
    }
}

Here is my main

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {

        Student s[]=new Student[2]; //I want to use an array of objects like this.

        Scanner name=new Scanner(System.in);
        Scanner ID=new Scanner(System.in);
        Scanner phoneNumber=new Scanner(System.in);


           int q=1;


                do{
               int i=0;


          System.out.println("Enter Name");

          String nameInput=name.nextLine();
          s[i].setName(nameInput);

          System.out.println("Enter ID");

          String IDInput=ID.nextLine();
          s[i].setID(IDInput);
          System.out.println("Enter Phone Number");

          int phoneNumberInput=phoneNumber.nextInt();

          s[i].setPhoneNumber(phoneNumberInput);
                i++;
                      } while(q!=1);



        System.out.println("Name:" +s[0].getName());
        System.out.println("Name:" +s[1].getName());
        System.out.println("Name:" +s[2].getName());

        System.out.println("ID:" +s[0].getId());
        System.out.println("ID:" +s[1].getId());
        System.out.println("ID:" +s[2].getId());

        System.out.println("Phone:" +s[0].getPhoneNumber());
        System.out.println("Phone:" +s[1].getPhoneNumber());
        System.out.println("Phone:" +s[2].getPhoneNumber());
     }


    }

Output:

Enter Name
John
Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Student.setName(String)" because "s[i]" is null
    at Main.main(Main.java:28)

*Edit Note after solve: The solution demonstrates how each array element, a[i] should be instantiated within a loop. This exact concept, I did not find in the other posts.

Fixed the faulty part:

int i=0;
while(i<n){

              s[i] = new Student();
              System.out.println("Enter Name");

              String nameInput = name.nextLine();
              s[i].setName(nameInput);

              System.out.println("Enter ID");

              String IDInput = ID.nextLine();
              s[i].setId(IDInput);
              System.out.println("Enter Phone Number");

              int phoneNumberInput = phoneNumber.nextInt();

              s[i].setPhoneNumber(phoneNumberInput);

              i++;
          }
Habeeb E Sadeed
  • 49
  • 7

1 Answers1

0

You created an empty array. You need to create a new student object for each element.

String nameInput=name.nextLine();
s[i] = new Student();
s[i].setName(nameInput);
egeorge
  • 612
  • 3
  • 11