class Exercise implements IGrade, IReadWrite{
	private int studentAnswer;
	private char grade;

	private final String question;
	private final int modelAnswer;

	public Exercise(String q, int a) {question = q; modelAnswer=a;}

	public void writeAnswer(int anAnswer) {studentAnswer=anAnswer;}
	public void readAnswer() {System.out.println("Student's answer is "+studentAnswer);}
	public void grade() {if (studentAnswer==modelAnswer) grade='A';else grade='F';}

	public void displayResult() {System.out.println("Student's answer is "+studentAnswer+", grade is: "+grade);} 
}