Grades.java

import javax.swing.JOptionPane;

public class Grades {
    
    public static void main(String[] args) {
        
        int mathGrade = 0;
        int historyGrade = 0;
        int scienceGrade = 0;
        double average = 0;
        
        mathGrade = Integer.parseInt(JOptionPane.showInputDialog("Enter math grade between 0 and 100!"));
        historyGrade = Integer.parseInt(JOptionPane.showInputDialog("Enter history grade between 0 and 100!"));
        scienceGrade = Integer.parseInt(JOptionPane.showInputDialog("Enter science grade between 0 and 100!"));
        
        // Compute average
        average = (mathGrade+historyGrade+scienceGrade)/3;
        
        // Perform if & else control
        if (average >= 60){
            JOptionPane.showMessageDialog(null, "Good job! Your average is " + average);
        } else{
            JOptionPane.showMessageDialog(null, "You need to do better! Your average is " + average);
        }
        
    }
}