Test Score Average Program In Java

I'm working on a homework assignment and I keep getting a compiler message this is the message

GradesAverage.java:44: error: variable totalgrade might not have been initialized
System.out.println("Over all you have " + totalgrade);
^
1 error

The homework is this Write a program that has variables to hold three test scores. The program should ask the user to enter three test scores and then assign the values entered to the variables. The program should display the average of the test stores and the letter grade that is assigned for the test score average. Use the grading scheme in the following table:

Test Score Average Letter Grade
90-100 A
80-89 B
70-79 C
60-69 D
Below 60 F

This is my code

import javax.swing.JOptionPane; // Needed for JOptionPane class
import java.util.Scanner; // Needed for the scanner class
public class GradesAverage
{
public static void main (String[] args)

[code]....