Using mutator and accessor methods in main.

Question

Would somebody explain to me exactly how mutator and accessor methods make a class and it's driver program work together. I understand the principle of encapsulation, but I'm obviously missing something. I get the syntax, but what actually happens? I'm hoping a fresh perspective on it will help me understand better.
I guess another way to ask the question could be: how do you use accessor and mutator methods in the main program that calls them?

Answer 1

>
the assignment says to have a
"reasonable set of accessor and mutator methods
whether or not you use them". So in my case I have
them written in the class but do not call them inthe
driver program. And like I said, the program does
what it's supposed to do.This class you're in worries me. I'm sure what
polytropos said is true: they're trying to make you
think about reuse. But adding to an API without cause
is widely considered to be a mistake, and there are
those who are strongly opposed to accessors/mutators
(or worse, direct field access) on OOP design grounds.The class is based on the book Java: Introduction to Computer Science and Progamming, by Walter Savitch. Until now I've been pretty happy with it. Another problem, to me anyway, is that so far we've done a few, cumulative programming projects per chapter. This time, there was one assignment for the whole chapter that is suppsoed to incorporate everything. But that's just me complaining.
Here is the code I have and that it looks like I'll be turning in... criticisms welcome.
Here is the class:
public class GradeProgram//open class
     private double quiz1;
     private double quiz2;
     private double mid;
     private double fin;
     private double finalGrade;
     private char letterGrade;
     public void readInput()//open readInput object
          do
               System.out.println("Enter the total points for quiz one.");
               quiz1 = SavitchIn.readLineInt();
               System.out.println("Enter the total points for quiz two.");
               quiz2 = SavitchIn.readLineInt();
               System.out.println("Enter the mid term score.");
               mid = SavitchIn.readLineInt();
               System.out.println("Enter final exam score.");
               fin = SavitchIn.readLineInt();
               if ((quiz1>10)||(quiz2>10)||(quiz1<0)||(quiz2<0))
               System.out.println("Quiz scores are between one and ten.  Re-enter scores");
               if ((mid>100)||(fin>100)||(mid<0)||(fin<0))
               System.out.println("Exam scores are between zero and one hundred.  Re-enter scores.");
          while ((quiz1>10)||(quiz2>10)||(quiz1<0)||(quiz2<0)||(mid>100)||(fin>100)||(mid<0)||(fin<0));
     }//end readInput object
     public void output()//open output object
          System.out.println();
          System.out.println("You entered:");
          System.out.println("Quiz 1: " + (int)quiz1);
          System.out.println("Quiz 2: " + (int)quiz2);
          System.out.println("Mid term: " + (int)mid);
          System.out.println("Final exam: " + (int)fin);
          System.out.println();
          System.out.println("Final grade: " + (int)percent() + "%");
          System.out.println("Letter grade: " + letterGrade());
     }//end output object
     public void set(double newQuiz1, double newQuiz2, double newMid, double newFin, double newFinalGrade, char newLetterGrade)
          if ((newQuiz1 >= 0)&&(newQuiz1 <= 10))
          quiz1 = newQuiz1;
          else
               System.out.println("Error: quiz scores are between zero and ten.");
               System.exit(0);
          if ((newQuiz2 >= 0)&&(newQuiz2 <= 10))
          quiz2 = newQuiz2;
          else
               System.out.println("Error: quiz scores are between zero and ten.");
               System.exit(0);
          if ((newMid >= 0)&&(newMid <= 100))
          mid = newMid;
          else
               System.out.println("Error: exam scores are between zero and one hundred.");
               System.exit(0);
          if ((newFin >= 0)&&(newFin <= 100))
          fin = newFin;
          else
               System.out.println("Error: exam scores are between zero and one hundred.");
               System.exit(0);
          letterGrade = newLetterGrade;
     public double getQuiz1()
          return quiz1;
     public double getQuiz2()
          return quiz2;
     public double getMid()
          return mid;
     public double getFin()
          return fin;
     public char getLetterGrade()
          return letterGrade;
     private double finalPercent()//open finalPercent object
          double quizPercent = (((quiz1 + quiz2) /2) * 10) / 4;
          if (((((quiz1 + quiz2) /2) * 10) % 4) >= 5)
               quizPercent++;
          double midPercent = mid / 4;
          if ((mid % 4) >= 5)
               midPercent++;
          double finPercent = fin / 2;
          if ((fin % 2) >= 5)
               finPercent++;
          finalGrade = (quizPercent + midPercent + finPercent);
          return (finalGrade);
     }//end final percent object
     private double percent()//open percent object - helping object
          double percentGrade = finalPercent();
          return (percentGrade);
     }//end percent object
     private char letterGrade()//open letterGrade object
          double letter = percent();
          if (letter >= 90)
               return ('A');
          else if (letter >= 80)
               return ('B');
          else if (letter >= 70)
               return ('C');
          else if (letter >= 60)
               return ('D');
          else
               return ('F');
     }//end letterGrade object
     private double quizScore()//open quizScore object
          double quizes = ((quiz1 + quiz2) /2) * 10;
          return (quizes);
     }// close quizScore object
}//end classAnd here is the driver program:
public class GradeProgramDemo
     public static void main(String[] args)
          String cont;
          do
               GradeProgram firstStudent = new GradeProgram();
               firstStudent.readInput();
               firstStudent.output();
               System.out.println();
               System.out.println("Enter more student grades?  Enter Y to continue");
               System.out.println("or press enter to quit.");
               cont = SavitchIn.readLine();
               System.out.println();
          while (cont.equalsIgnoreCase("y"));