How To Use Class Method To Calculate Average Of All Values In An Array

Question

I'm trying to create a class that prints out Student details and I wish to know how to take an int array and calculate the average of all their marks.

Here's what I have so far:

public class Student {
    private int id;
    private String name;
    private String course;
    private int[] marks;

    Student (int id, String name, String course, int [] marks) {
    // constructor which creates a student according to the specified parameters
       this.id = id;
       this.name = name;
       this.course = course;
       this.marks = marks;
    }

    int average () {
    //  calculates and returns the average mark for the student
        return marks / 5; // error: the operator / is undefined for the argument type int[]
    }

    void print () {
    // prints student details
        System.out.println("Student ID: "+id+"\n");
        System.out.println("Student Name: "+name+"\n");
        System.out.println("Course enrolled on: "+course+"\n");
        System.out.println("Student mark: "+marks+"\n"); // This prints a hashcode for some reason
}

}

My question, specifically, is how do I return the average of the int[] marks in the "int average()" method (without changing the header or parameters in the parenthesis)?

public class T3Main {
public static void main(String[] args) {
    Student s1 = new Student(1234, "Joe Bloggs", "Computer Studies", new int[] {67, 55, 78, 72, 50});
    Student s2 = new Student(2341, "Sue White", "Computer Science", new int[] {57, 85, 58, 49, 61});
    Student s3 = new Student(3412, "Ben Black", "Software Engineering", new int[] {71, 45, 66, 70, 51});
    s1.print();
    s2.print();
    s3.print();
}

}

Answer 1

You can not use operator with array, thus marks / 5 is incorrect. You need to do sum of all array items and store it in separate variable and then divide it with 5 (length of array). You may need to be careful about empty or null array.

double sum = 0d;
for(int item : marks) {
    sum += item;
}
return sum / marks.length;

---

Moreover following statement print string representation of array and not it's content.

System.out.println("Student mark: "+marks+"\n");

You can use following way to print array,

System.out.println("Student mark: "+ Arrays.toString(marks) +"\n");

Answer 2

With Java 8:

Arrays.stream(marks).average().getAsDouble();

And you can convert to int (rounded down) with (int)

(int)Arrays.stream(marks).average().getAsDouble();

Answer 3

import java.util.stream.*;

It's in the package java.util.stream

Example:

int[] marks = {10,20,30,40,50};
int sum = IntStream.of(marks).sum();
System.out.println("The sum is " + sum);

Answer 4

Since int[] is an object and contains an array with your marks, the / operator is not defined for this type. You will have to divide the total sum of the marks to their number to find out the average:

double average () {
    double markSum = 0;
    double average;
    int i;
    for (i = 0; i < marks.length; i++) {
        markSum = markSum + marks[i];
    }
    average = markSum / marks.length;
    return average;
}

Also, please note that usually the correct data type to use here is double , because int might get you incorrect (rounded) results: in case marks = [1, 2, 3, 4] the average is 2.5 , but by using int average() you will get 2 .