Here is a code that accepts the number of students and their marks and display their respective grades.

import java.util.*;

public class StudentMarks{

        double totalMarks;
        String grade;

        public void setTotalMarks(double totalMarks){
        this.totalMarks=totalMarks;
        }
        public double getTotalMarks(){
        return totalMarks;
        }
        public void setGrade(String grade){
        this.grade=grade;
        }
        public String getGrade(){
        return grade;
        }
        public static void main(String[]args){
                Scanner input=new Scanner(System.in);
                System.out.print("Enter number of students: ");
                int num=input.nextInt();
                StudentMarks data[]=new StudentMarks[num];
                for (int i=0; i<data.length; i++) {
                System.out.println("Enter marks");
                double marks=input.nextDouble();
                data[i] = new StudentMarks();
                data[i].setTotalMarks(marks);
                if(marks>=90&&marks<=100){
                    data[i].setGrade("A");
                }
                else if(marks>=80&&marks<=89){
                    data[i].setGrade("B");
                }
                else if(marks>=70&&marks<=79){
                    data[i].setGrade("C");
                }
                else if(marks>=60&&marks<=69){
                    data[i].setGrade("D");
                }
                else{
                    data[i].setGrade("F");
                }

                }

                for(int i=0;i<num;i++){
                StudentMarks show = data[i];
                System.out.println(show.getTotalMarks()+":"+show.getGrade());
                }
            }
        }