Java execute problem-Student ID class and ShowStudent class paired together

[blewie07]

Create a class named Student. A student has fields for an ID number, number of credit hours earned, and number of points earned. (For example, many schools compute grade point averages based on a scale of 4, so a three-credit-hour class in which a student earns an A is worth 12 points. Also, create a class variable called lastStudentID which holds the last student ID number assigned to a student. Initialize it to 0. Each new student is assigned a student ID by adding one to this number. Update lastStudentID each time a student is created.

Next, include methods to assign values to all fields separately. For example, one method should assign ID number, another should assign credit hours earned, etc. A Student also has a field for grade point average. Include a method to compute the grade point average field by divinding points by credit hours earned. Write methods to display the values in each Student field.

Write a class named ShowStudent that instantiates a Student object from the class you created above. Set the necessary values and compute the Student grade point average, and then display all the values associated with the Student. Create three different students with different values.

I write it and it executes but then has errors in it..I dont know what the issue is I am using NetBeans

 package student;
 
/**
 *
 * @author rlewis07
 */
javac -cp . *.java 
...
java -cp . ShowStudent
 class Student
{
    // the private data members
    private int IDnumber;
    private int hours;
    private int points;
 
    // constructor added in last part of project
    Student()
    {
        IDnumber = 77375;
        points = 12;
        hours = 3;
    }
    // end of constructor
 
    // the public get and set methods
    public void setIDnumber(int number)
    {
        IDnumber = number;
    }
 
 
    public int getPoints()
    {
        return points;
    }
 
    // methods to display the fields
    public void showIDnumber()
    {
        System.out.println("ID Number is: " + IDnumber);
    }
 
    public void showHours()
    {
        System.out.println("Credit Hours: " + hours);
    }
 
    public void showPoints()
    {
        System.out.println("Points Earned: " + points);
    }
 
    public double getGradePoint()
    {
        return (double)points / hours;
    }
 
}
 
 

my showStudent Code:

package student;
 
/**
 *
 * @author rlewis07
 */
 public class ShowStudent
{
    public static void main (String args[])
    {
        Student pupil = new Student();// 2 cannot resolve sybmol... points to 'S' in Student 
 
 
        pupil.showIDnumber();
        pupil.showPoints();
        pupil.showHours();
        System.out.println("The grade point average of the studnet created by constructor is "
            + pupil.getGradePoint()+"\n\n");
 
        Student s2 = new Student();// 2 cannot resolve sybmol points to 'S in Student
        s2.setIDnumber(12345);
        s2.setPoints(66);
        s2.setHours(20);
        s2.showIDnumber();
        s2.showPoints();
        s2.showHours();
        System.out.println("The grade point average of another student is "
            + s2.getGradePoint()+"\n");
 
    }
}
 

[Frinavale]

It has been a long time since I've used Java but I believe in the file that contains the ShowStudent class you should be importing the student using the import keyword....

Check out this tutorial about Using Package Members.

-Frinny

[blewie07]

Why if I do not have the constructor in my student class does it not run how do I assign the variables with out using a constructor? It runs but the values do not assign.
Looks like this:
run:
Student 1
ID Number is: 0
Points Earned: 0
Credit Hours: 0
Grade point average: NaN

[Frinavale]

Your variables:

    private int IDnumber;
    private int hours;
    private int points;

Have a private scope which means that they are not accessible outside of the class where they were declared.

There are a few ways that you can chose to set these private variables from outside of the class (in your ShowStudent class's main method):

1. Provide a constructor that lets you set them (which you said you aren't interested in)
2. Change the scope of your variables to public so that you can access them outside of the class
3. Implement public set... methods that can be called to set the private variables

In the code you posted here you are calling the following functions:

  s2.setIDnumber(12345);
  s2.setPoints(66);
  s2.setHours(20);
 

Which implies to me that you are going for the last option:

implement public set... methods that can be called to set the private variables

This is actually a very smart way to implement the class because your set methods could do validation on the data that is about to be set to ensure that it is correct.

This, used in combination with the get methods, is a good safe way to ensure that the data in your class is correct.

So, in order to interact with the private member points from outside the class you are going to need the following 2 functions:

public void setPoints(int newPointsValue)
{
  points = newPointsValue;
}
public int getPoints()
{
  return points;
}

That way you have the ability to set the private points member and the ability to get the value of the private points member from code that uses this class.

If you want to ensure that the points value contains a positive number you can do validation in the setPoints method to ensure that this is the case:

public void setPoints(int newPointsValue)
{
  if(newPointsValue < 0){
   // here you need to throw exception so that the code stops executing
   // you need a try catch block in the calling code that 
   // catches the exception that you throw so that your application doesn't crash
  }
  points = newPointsValue;
}
public int getPoints()
{
  return points;
}

Right now you are missing the set method according to the code that you posted which is why you can't set the values.


Now, if you were to change the scope to public you will be able to access the variables outside of the class in the ShowStudent class's main method.

After changing the scope of the class member variables to public, you would be able to set the members directly:

  Student pupil = new Student();
  pupil.IDnumber=12345;
  pupil.points = 66;
  pupil.hours = 20;
 

However, because you are not using the set method to set the values you will not be able to do validation to ensure that the data provided for the members is correct according to your business rules.

-Frinny