Creating an object instance that is to save user input to another class

[Chris Morris]

Being I am a beginner, I am sure the subject's explanation makes little to no sense. I hope that the code can explain the story better. I am certainly not looking for someone to do the code for me, just to maybe guide me in the right direction since I am absolutely lost at this point.

The exercise - not a homework assignment, do not worry - asks to create two classes; a CollegeCourse class and a Student Class. The CollegeCourse class is supposed to have data fields for a course ID, grade, and credit hours and then set and get methods for each. The Student class, which is where I believe I am messing up, contains a data field for a student ID and 5 CollegeCourse objects by using an array. This class requires set and get methods as well, although I am having trouble with the set and get methods for the object array. The third class, InputGrades, is the one that contains the main class and utilizes the first two classes. The third class is incomplete as of now because I have not figured out how to properly use the objects, especially the object array within the Student class.

Thank you in advance and feel free to offer any critiques, even if unrelated to topic (e.g. poor coding, etc.).

public class CollegeCourse{
    
    // Declares private data fields
    private String id;
    private String grade;
    private int creditHours;
    
    // get methods for all data fields
    public String getID(){
        return id;
    }
    public String getGrade(){
        return grade;
    }
    public int getCreditHours(){
        return creditHours;
    }
    
    // get methods for all data fields
    public void setID(String id){
        this.id = id;
    }
    public void setGrade(String grade){
        this.grade = grade;
    }
    public void setCreditHours(int creditHours){
        this.creditHours = creditHours;
    }
}

public class Student{
    
    // Declares a String data field
    private String id;
    // Declares 5 CollegeCourse objects and names the array
    // collegeCourseArray
    CollegeCourse[] collegeCourseArray = new CollegeCourse[5];
    
    // get and set methods for String "id"
    public String getID(){
        return id;
    }
    public void setID(String id){
        this.id = id;
    }
    
    // THIS IS WHERE I THINK I AM GOING WRONG!!!!!
    // get and set methods for CollegeCourse
    public CollegeCourse getCourse(int arrayInput){
        return collegeCourseArray[arrayInput];
    }
    public void setCourse(CollegeCourse student, int course){
        collegeCourseArray[course] = new CollegeCourse();
    }
}

import java.util.*;
public class InputGrades{
    public static void main(String[] args){
        
        // Scanner, int and String declared
        Scanner keyboard = new Scanner(System.in);
        int y=0;
        String entry;
        
        // Ten Student objects declared with the
        // array name studentObject
        Student[] studentObject = new Student[10];
        // CollegeCourse object declared
        CollegeCourse collegeObject = new CollegeCourse();
        
        // for loop to create each object individually
        for(int x=0; x<studentObject.length; ++x){
            studentObject[x] = new Student();
            for(int i=0; i<5; ++i){
                studentObject[x].setCourse(collegeObject, i);
            }
        }
        
        // for loop to set data for the student
        // (i.e. Student ID, Grade, and Credit Hours)
        // 
        for(int x=0; x<studentObject.length; x++){
            System.out.print("Please enter the ID for the student #" + (x+1) + ": ");
            studentObject[x].setID(keyboard.nextLine());
            for(int i=0; i<5; ++i){
                System.out.print("Please enter the Credit Hours of course #" + (i+1) + ": ");
                collegeObject.setCreditHours(keyboard.nextInt());
                keyboard.nextLine();
                System.out.print("Please enter the Grade for that course: ");
                collegeObject.setGrade(keyboard.nextLine());
                System.out.println(studentObject[x].getCourse(i));
            }
            keyboard.nextLine();
        }
    }
}

[Campbell Ritchie]

You need constructors for those classes. And a toString() method.
Example

public class Student
{
   private int coursesToDate;
   private String name;
   private String id;
   private CollegeCourse[] collegeCourseArray;

   public Student(String name, String id)
   {
      this.name = name;
      this.id = id;
      collegeCourseArray = new collegeCourse[5];
      coursesToDate = 0;
   }

   @Override public String toString()
   {
      StringBuilder sb = new StringBuilder("Student: " + name);
      sb.append(" ").append(id).append(" reading ");
      for(int i = 0; i < collegeCourseArray.length && collegeCourseArray[i] != null; i++)
      {
          sb.append(collegeCourseArray[i].getID()).append(String.format("%n"));
      }
      return sb.toString();
   }

/**
 * This method must not be used more than 5 times, or you will suffer an Exception
 */
   public void addNewCourse(Course c)
   {
      collegeCoursesArray[coursesToDate++] = c;
   }
}

This class uses similar fields to yours, initialising the array in the constructor, not the declaration. I would have added name as a field.
Get a StudentDemo class, and use this sort of code to run your Student object

Student s = new Student("Campbell Ritchie", "a123456");
s.addNewCourse(new CollegeCourse("Maths", "M101", 99);
s.addNewCourse(new CollegeCourse("Trigonometry", "MT123", 55);
System.out.println(s)

You will have to look for spelling errors; I think I had a small c in CollegeCourse somewhere. You will also notice I have missed out the get and set methods. Write equals() and hashCode() methods too.

Using the sort of code in the second block, you can observe the workings of the class, and play with it. That's the best way to learn.

[Campbell Ritchie]

... and welcome to the Ranch

[Chris Morris]

Thank you for the response!

Your suggestions were great and I will definitely put them to use as soon as I get a chance. The constructor suggestion seems to be the real link between the two classes. I think I got confused because of the language used by the exercise. It didn't mention using a constructor but gave direct orders for everything else so I assumed there shouldn't be a constructor. Although it didn't seem to make sense until you mentioned the constructor and override toString() method. I am unfamiliar with the hashCode() method, although will definitely do some research. As soon as I get it figured out or make progress, I will post an update. Thanks again!

Chris

[Campbell Ritchie]

You're welcome

I read somewhere recently (maybe here) that the Sun/Oracle convention is always to give a class a constructor. Even for classes you don't want to instantiate. I would agree; it is a good convention for every class to have a constructor explicitly written.

[Prince Sewani]

The one by Campbell is much optimized indeed.. but your design also didn't had any problem.. the only problem area that
I can observe from your code is here :

        // CollegeCourse object declared  
        CollegeCourse collegeObject = new CollegeCourse();  
          
        // for loop to create each object individually  
        for(int x=0; x<studentObject.length; ++x){  
            studentObject[x] = new Student();  
            for(int i=0; i<5; ++i){  
                studentObject[x].setCourse(collegeObject, i);  
            }  
        } 

you were using the same CollegeCourse object for all students...and then setting the values for the students..and every next value overrides the
previous one..as indeed those are instance values but also are the instances to the same reference (something you must know when using objects)

Regards
Prince

Chris Morris wrote:Being I am a beginner, I am sure the subject's explanation makes little to no sense. I hope that the code can explain the story better. I am certainly not looking for someone to do the code for me, just to maybe guide me in the right direction since I am absolutely lost at this point.

The exercise - not a homework assignment, do not worry - asks to create two classes; a CollegeCourse class and a Student Class. The CollegeCourse class is supposed to have data fields for a course ID, grade, and credit hours and then set and get methods for each. The Student class, which is where I believe I am messing up, contains a data field for a student ID and 5 CollegeCourse objects by using an array. This class requires set and get methods as well, although I am having trouble with the set and get methods for the object array. The third class, InputGrades, is the one that contains the main class and utilizes the first two classes. The third class is incomplete as of now because I have not figured out how to properly use the objects, especially the object array within the Student class.

Thank you in advance and feel free to offer any critiques, even if unrelated to topic (e.g. poor coding, etc.).

public class CollegeCourse{
    
    // Declares private data fields
    private String id;
    private String grade;
    private int creditHours;
    
    // get methods for all data fields
    public String getID(){
        return id;
    }
    public String getGrade(){
        return grade;
    }
    public int getCreditHours(){
        return creditHours;
    }
    
    // get methods for all data fields
    public void setID(String id){
        this.id = id;
    }
    public void setGrade(String grade){
        this.grade = grade;
    }
    public void setCreditHours(int creditHours){
        this.creditHours = creditHours;
    }
}

public class Student{
    
    // Declares a String data field
    private String id;
    // Declares 5 CollegeCourse objects and names the array
    // collegeCourseArray
    CollegeCourse[] collegeCourseArray = new CollegeCourse[5];
    
    // get and set methods for String "id"
    public String getID(){
        return id;
    }
    public void setID(String id){
        this.id = id;
    }
    
    // THIS IS WHERE I THINK I AM GOING WRONG!!!!!
    // get and set methods for CollegeCourse
    public CollegeCourse getCourse(int arrayInput){
        return collegeCourseArray[arrayInput];
    }
    public void setCourse(CollegeCourse student, int course){
        collegeCourseArray[course] = new CollegeCourse();
    }
}

import java.util.*;
public class InputGrades{
    public static void main(String[] args){
        
        // Scanner, int and String declared
        Scanner keyboard = new Scanner(System.in);
        int y=0;
        String entry;
        
        // Ten Student objects declared with the
        // array name studentObject
        Student[] studentObject = new Student[10];
        // CollegeCourse object declared
        CollegeCourse collegeObject = new CollegeCourse();
        
        // for loop to create each object individually
        for(int x=0; x<studentObject.length; ++x){
            studentObject[x] = new Student();
            for(int i=0; i<5; ++i){
                studentObject[x].setCourse(collegeObject, i);
            }
        }
        
        // for loop to set data for the student
        // (i.e. Student ID, Grade, and Credit Hours)
        // 
        for(int x=0; x<studentObject.length; x++){
            System.out.print("Please enter the ID for the student #" + (x+1) + ": ");
            studentObject[x].setID(keyboard.nextLine());
            for(int i=0; i<5; ++i){
                System.out.print("Please enter the Credit Hours of course #" + (i+1) + ": ");
                collegeObject.setCreditHours(keyboard.nextInt());
                keyboard.nextLine();
                System.out.print("Please enter the Grade for that course: ");
                collegeObject.setGrade(keyboard.nextLine());
                System.out.println(studentObject[x].getCourse(i));
            }
            keyboard.nextLine();
        }
    }
}