Find highest, lowest and average marks

public class Marks {
    public static void main(String[] args) {
        int[] marks = {72, 85, 61, 90, 77}; // example values
        int max = marks[0], min = marks[0], sum = 0;
        for (int mark : marks) {
            if (mark > max) max = mark;
            if (mark < min) min = mark;
            sum += mark;
        }
        double average = (double) sum / marks.length;
        System.out.println("Highest = " + max);
        System.out.println("Lowest = " + min);
        System.out.println("Average = " + average);
    }
}

Replace the example array with the 50 students' marks. Initializing max and min from the first element avoids assuming marks are non-negative. A single pass calculates all three values: O(n) time and O(1) extra space.