How can i repeat statement "enter marks or grade" with in while loop.In this case every time control back to start of loop to enter subject again?

How can i repeat statement "enter marks or grade" with in while loop.In this case every time control back to start of loop. and i want to repeat enter marks until user want to leave?

public class Marks2 {
    public static void main(String args[]){
        Scanner s=new Scanner(System.in);
        System.out.println("Here is Subject list");
        System.out.println("1-Physics");
        System.out.println("2-Math");
        System.out.println("3-computer");
        boolean input=true;

        while (input){
            System.out.println("Enter subject number here");
            String sub=s.nextLine();

            if(sub.equals("1")) {
                System.out.println("Physics");
                System.out.println("");
                System.out.println("Enter marks  /Enter change for change  /Enter exit for leave");
                String change1 = null;
                String change2 = null;
                int marks = 0;
                try {
                    change1 = s.nextLine();
                    marks = Integer.parseInt(change1);
                } catch (Exception e) {
                    System.out.println("Please enter only string value");
                    change2 = s.nextLine();
                    if (change2.equals("change")) {
                        continue;
                    } else if (change2.equals("exit")) {
                        System.exit(0);
                    }
                }

                if(marks<40){
                    System.out.println("Student is fail");
                }
                else if(marks==40){
                    System.out.println("Student is fail he need more practice");
                }
                else if(marks<70){
                    System.out.println("need more practice but also good");
                }
                else if(marks==70){
                    System.out.println("Good");
                }
                else if(marks<90){
                    System.out.println("Good but also Excellent");
                }
                else if(marks==90){
                    System.out.println("Excellent");
                }
                else if(marks<100){
                    System.out.println("Outstanding");
                }
                else if(marks==100){
                    System.out.println("Good but also excellent");
                }
                else if(change1.equals("change")){
                    continue;
                }
                else if(change2.equals("exit")){
                    System.exit(0);
                }
                else  {
                    System.out.println("");
                }
                continue;
            }
        }
    }
}

After continue control went to start of loop and ask to enter subject again. Is it possible to enter grade until user wants to leave?

You need another while loop inside the first one, if i understand right, you want to change the subject once you enter change? if that is the case then this will work:

public static void main(String args[])
{
Scanner s = new Scanner(System.in);
System.out.println("Here is Subject list");
System.out.println("1-Physics");
System.out.println("2-Math");
System.out.println("3-computer");
setSubject:
while (true)
{
System.out.println("Enter subject number here");
String sub = s.nextLine();
if (sub.equals("1"))
{
System.out.println("Physics");
int marks = 0;
while (true)
{
System.out.println("Enter marks  /Enter change for change  /Enter exit for leave");
if (s.hasNextInt())
{
marks = s.nextInt();
s.nextLine();
} else
{
String command = s.nextLine();
if (command.equalsIgnoreCase("exit")) break setSubject;
else if (command.equalsIgnoreCase("change")) continue setSubject;
else
{
System.out.println("Please enter a valid option");
continue;
}
}
if (marks < 40)
{
System.out.println("Student is fail");
} else if (marks == 40)
{
System.out.println("Student is fail he need more practice");
} else if (marks < 70)
{
System.out.println("need more practice but also good");
} else if (marks == 70)
{
System.out.println("Good");
} else if (marks < 90)
{
System.out.println("Good but also Excellent");
} else if (marks == 90)
{
System.out.println("Excellent");
} else if (marks < 100)
{
System.out.println("Outstanding");
} else if (marks == 100)
{
System.out.println("Good but also excellent");
} else
{
System.out.println("");
}
}
}
}
}

A Sample Run

Here is Subject list
1-Physics
2-Math
3-computer
Enter subject number here
1
Physics
Enter marks  /Enter change for change  /Enter exit for leave
change
Enter subject number here
1
Physics
Enter marks  /Enter change for change  /Enter exit for leave
50
need more practice but also good
Enter marks  /Enter change for change  /Enter exit for leave
60
need more practice but also good
Enter marks  /Enter change for change  /Enter exit for leave
exit
Process finished with exit code 0

With one while loop:

public static void main(String args[])
{
Scanner s = new Scanner(System.in);
System.out.println("Here is Subject list");
System.out.println("1-Physics");
System.out.println("2-Math");
System.out.println("3-computer");
String subject = "";
int marks = 0;
while (true)
{
if (subject.isEmpty())
{
System.out.println("Enter subject number here");
subject = s.nextLine();
}
if (subject.equals("1"))
{
System.out.println("Physics");
System.out.println("Enter marks  /Enter change for change  /Enter exit for leave");
if (s.hasNextInt())
{
marks = s.nextInt();
s.nextLine();
} else
{
String command = s.nextLine();
if (command.equalsIgnoreCase("exit")) break ;
else if (command.equalsIgnoreCase("change")) {
subject = "";
continue ;
}
else
{
System.out.println("Please enter a valid option");
continue;
}
}
if (marks < 40)
{
System.out.println("Student is fail");
} else if (marks == 40)
{
System.out.println("Student is fail he need more practice");
} else if (marks < 70)
{
System.out.println("need more practice but also good");
} else if (marks == 70)
{
System.out.println("Good");
} else if (marks < 90)
{
System.out.println("Good but also Excellent");
} else if (marks == 90)
{
System.out.println("Excellent");
} else if (marks < 100)
{
System.out.println("Outstanding");
} else if (marks == 100)
{
System.out.println("Good but also excellent");
} else
{
System.out.println("");
}
marks = 0;
}
}
}