Calling a constructor with object array

Question

I need to create an object array and read the values of the elements in the constructor from console. I am totally confused how to do it.Can anyone give a clarity about how to do it

public class Student {
    int id;
    String name;
    double marks;

    public Student(int id, String name, double marks) {
        id = this.id;
        name = this.name;
        marks = this.marks;
    }
}

public class Solution {
    public static void main(String[],args)
    {
      Scanner sc = new Scanner(System.in);
      int n=sc.nextInt();
      Student[] arr=new Student[n];
      for(int i=0;i<n;i++)
      {
         int x =sc.nextInt();
         String y=sc.nextLine();
         double z=sc.nextDouble();
         arr[i]=arr.Student(x,y,z);
      }
    }
}

I am confused on how to call the constructor. Can anyone help me?

Additionally, you're setting variables incorrectly in your constructor: id = this.id; should be this.id = id; (same for the other 2 variables) — ernest_k
– ernest_k, Commented Feb 17, 2019 at 8:59

abdulwasey20 · Accepted Answer · 2019-02-17 09:15:32Z

1

You can do one of two things:

1.Create a temporary object by calling the constructor and then adding that object in the array:

Student temp= new Student(x,y,z);
arr[i]=temp;

2.Directly instantiate a new object and add it in the array like this:

arr[i]=new Student(x,y,z);

Both methods will work fine, but it is recommended to use method 2 because you should not allocate memory to a temp object when clearly you can achieve the goals without doing so

answered Feb 17, 2019 at 9:15

abdulwasey20

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Comments

N.B · Accepted Answer · 2019-02-17 09:26:37Z

1

Instead of:

arr[i]=arr.Student(x,y,z);

Do:

arr[i]=new Student(x,y,z);

Why? Because, Each object in the array is an instance of Student class

answered Feb 17, 2019 at 9:26

N.B

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Comments

Kushal · Accepted Answer · 2019-02-17 12:41:20Z

Your constructor is declared wrongly. this is always used to refer to the instance variable. Change your constructor to this:

public class Student {
int id;
String name;
double marks;

public Student(int id, String name, double marks) {
    this.id = id;
    this.name = name;
    this.marks = marks;
} }

public class Solution {
    public static void main(String[],args)
    {
      Scanner sc = new Scanner(System.in);
      int n=sc.nextInt();
      Student[] arr=new Student[n];
      for(int i=0;i<n;i++)
      {
         int x =sc.nextInt();
         String y=sc.nextLine();
         double z=sc.nextDouble();
         arr[i]= new Student(x,y,z); //no need to create an object for arr
      }
    }
}

Wing Kui Tsoi · Accepted Answer · 2019-02-17 09:30:33Z

-1

Because your constructor is wrong.

public class Student {
    int id;
    String name;
    double marks;

    public Student(int id, String name, double marks) {
        this.id = id;
        this.name = name;
        this.marks = marks;
   }
}

answered Feb 17, 2019 at 9:30

Wing Kui Tsoi

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