Implementing toString with information from another class

[Brandon Williams]

For this homework, we have to implement a HashMap database.  When I run the program, I get a message dialog showing the following:  I believe I'm having an issue bringing the information to my toString method in my Student class, but I can't find the error.
   
   Name: Name:, Major: Major:, GPA: 4.0
   
   Anyone know what am I doing wrong here?
   

   import java.awt.GridLayout;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import java.util.HashMap;
    
    import javax.swing.JButton;
    import javax.swing.JComboBox;
    import javax.swing.JFrame;
    import javax.swing.JLabel;
    import javax.swing.JOptionPane;
    import javax.swing.JTextField;
    import javax.swing.SwingUtilities;
    
    public class GUI extends JFrame implements ActionListener {
        private JLabel id = new JLabel("Id: ");
        private JLabel name = new JLabel("Name: ");
        private JLabel major = new JLabel("Major: ");
        private JLabel selection = new JLabel("Choose Selection: ");
        private JTextField id_text = new JTextField();
        private JTextField name_text = new JTextField();
        private JTextField major_text = new JTextField();
        private String[] choices1 = { "Insert", "Delete", "Find", "Update" };
        private String[] choices2 = { "A", "B", "C", "D", "F" };
        private String[] choices3 = { "3", "6" };
        private JComboBox<String> cb1 = new JComboBox<String>(choices1);
        private JComboBox<String> cb2 = new JComboBox<String>(choices2);
        private JComboBox<String> cb3 = new JComboBox<String>(choices3);
        private JButton process = new JButton("Process Request");
        private HashMap<String, Student> database = new HashMap<String, Student>();
    
        public GUI() {
            super("Project 4");
            setSize(300, 200);
            setResizable(false);
            setLayout(new GridLayout(5, 2));
            add(id);
            add(id_text);
            add(name);
            add(name_text);
            add(major);
            add(major_text);
            add(selection);
            add(cb1);
            add(process);
            setVisible(true);
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            cb1.addActionListener(this);
            process.addActionListener(this);
    
        }
    
        @Override
        public void actionPerformed(ActionEvent e) {
            int selections = cb1.getSelectedIndex();
            if (e.getSource() == process) {
                String stringID = id_text.getText();
                if (stringID.length() == 0) {
                    displayMessage("Enter id Field!");
                    return;
                }
                if (selections == 0) {
                    if (database.containsKey(stringID)) {
                        displayMessage("ID already exists.");
                        return;
                    }
                    String name_String = name.getText();
                    String major_String = major.getText();
                    if (name_String.length() == 0) {
                        displayMessage("Enter name");
                        return;
                    }
                    if (major_String.length() == 0) {
                        displayMessage("Enter major");
                        return;
                    }
                    database.put(stringID, new Student(name_String, major_String));
                    displayMessage("Student Information Added!");
                } else {
                    if (!database.containsKey(stringID)) {
                        displayMessage("ID not found");
                        return;
                    }
    
                    if (selections == 1) {
                        Student student = database.get(stringID);
                        database.remove(stringID);
                        displayMessage("Student deleted");
    
                    } else if (selections == 3) {
                        String grade = (String) JOptionPane.showInputDialog(null, "Choose grade: ", "Choose grade",
                                JOptionPane.QUESTION_MESSAGE, null, choices2, choices2[0]);
                        int credits = Integer.parseInt((String) JOptionPane.showInputDialog(null, "Choose credits: ",
                                "Choose credits", JOptionPane.QUESTION_MESSAGE, null, choices3, choices3[0]));
                        Student student = database.get(stringID);
                        student.courseCompleted(grade, credits);
                        displayMessage("Student Information updated");
    
                    } else if (selections == 2) {
                        Student student = database.get(stringID);
                        displayMessage(student.toString());
                    }
                }
    
            }
        }
    
        public void displayMessage(String s) {
            JOptionPane.showMessageDialog(null, s);
        }
    
        public static void main(String[] args) {
            SwingUtilities.invokeLater(new Runnable() {
    
                @Override
                public void run() {
                    new GUI();
                }
            });
    
        }
    }
    
    public class Student {
        private String studentName;
        private String studentMajor;
        private int credits;
        private int numGrade;
        private boolean completed = false;
    
        public Student(String studentName, String studentMajor) {
        this.studentName = studentName;
        this.studentMajor = studentMajor;
        credits = 0;
        numGrade = 0;
    
        }
        public void courseCompleted(String courseGrade, int creditHours) {
            int grade = 0;
            if ("A".equals(courseGrade)){
                grade = 4;}
    
            else if ("B".equals(courseGrade)){
                grade = 3;}
    
            else if ("C".equals(courseGrade)){
                grade = 2;}
    
            else if ("D".equals(courseGrade)){
                grade = 1;}
    
            else if ("F".equals(courseGrade)){
                grade = 0;}
    
            credits += creditHours;
            numGrade += (grade*creditHours);
            completed = true;
        }
        @Override
        public String toString(){
            if (!completed) {
                return "Name: " +studentName + ", Major: " + studentMajor + ", GPA:  4.0"; }
            double gpa = numGrade / credits;
            return "Name: " +studentName + ", Major: " + studentMajor + ", GPA:  " + gpa; }
    
    
        }

[Liutauras Vilda]

I don't think you should have some logic within toString() method. I mean if statements or anything similar.
toString() method supposed to print field/-s values of a given time when the method is invoked.

I don't think this is the cause of this issue you are facing, but first I'd fix that and look further what the issue might be.

[Carey Brown]

I don't see any obvious problems here. I suspect the problem is in your database code.

[Rob Camick]

I believe I'm having an issue bringing the information to my toString method in my Student class

What is with all the code???

If you want to test a method of a class then all you need to do is create an instance of the class and then invoke the method of the class.

It works fine for me:

  public class Student
  {
        private String studentName;
        private String studentMajor;
        private int credits;
        private int numGrade;
        private boolean completed = false;

        public Student(String studentName, String studentMajor)
        {
        this.studentName = studentName;
        this.studentMajor = studentMajor;
        credits = 0;
        numGrade = 0;

        }

        public void courseCompleted(String courseGrade, int creditHours)
        {
            int grade = 0;
            if ("A".equals(courseGrade)){
                grade = 4;}

            else if ("B".equals(courseGrade)){
                grade = 3;}

            else if ("C".equals(courseGrade)){
                grade = 2;}

            else if ("D".equals(courseGrade)){
                grade = 1;}

            else if ("F".equals(courseGrade)){
                grade = 0;}

            credits += creditHours;
            numGrade += (grade*creditHours);
            completed = true;
        }

        @Override
        public String toString()
        {
            if (!completed)
            {
                return "Name: " +studentName + ", Major: " + studentMajor + ", GPA:  4.0";
            }

            double gpa = numGrade / credits;
            return "Name: " +studentName + ", Major: " + studentMajor + ", GPA:  " + gpa;
        }

	public static void main(String[] args) throws Exception
	{
		Student student = new Student("someName", "someMajor");
		System.out.println(student);
	}

}

[Brandon Williams]

The problem wasn't with the code compiling, rather it was with my toString not having the correct information in it.  Anyways, I figured it out.  I had my name_texy pointed to my JLabel instead of the text box.  Thanks all!

Rob Camick wrote:

I believe I'm having an issue bringing the information to my toString method in my Student class

What is with all the code???

If you want to test a method of a class then all you need to do is create an instance of the class and then invoke the method of the class.

It works fine for me:

  public class Student
  {
        private String studentName;
        private String studentMajor;
        private int credits;
        private int numGrade;
        private boolean completed = false;

        public Student(String studentName, String studentMajor)
        {
        this.studentName = studentName;
        this.studentMajor = studentMajor;
        credits = 0;
        numGrade = 0;

        }

        public void courseCompleted(String courseGrade, int creditHours)
        {
            int grade = 0;
            if ("A".equals(courseGrade)){
                grade = 4;}

            else if ("B".equals(courseGrade)){
                grade = 3;}

            else if ("C".equals(courseGrade)){
                grade = 2;}

            else if ("D".equals(courseGrade)){
                grade = 1;}

            else if ("F".equals(courseGrade)){
                grade = 0;}

            credits += creditHours;
            numGrade += (grade*creditHours);
            completed = true;
        }

        @Override
        public String toString()
        {
            if (!completed)
            {
                return "Name: " +studentName + ", Major: " + studentMajor + ", GPA:  4.0";
            }

            double gpa = numGrade / credits;
            return "Name: " +studentName + ", Major: " + studentMajor + ", GPA:  " + gpa;
        }

	public static void main(String[] args) throws Exception
	{
		Student student = new Student("someName", "someMajor");
		System.out.println(student);
	}

}

[Rob Camick]

The problem wasn't with the code compiling,

I never said it was.

rather it was with my toString not having the correct information in it.

Exactly and I showed you how to debug your code in a couple of statements instead of "guessing" that the problem was with the toString() method.

The point is to learn to simply the problem so you can concentrate on finding the problem instead of guessing.

Did you run the code I provided for you?

If you did you would know the problem is not with the toString() method, but with how you create the Student class. This will allow you to narrow done where in the code to look for the problem!

[Fred Kleinschmidt]

You need to do some serious re-design. As your code now stands, a Student can take at most one course, and you have no way of specifying what course that is!

[Campbell Ritchie]

Consider replacing most of line 137‑157 with a switch statement.
Please reconsider the position of your empty lines. One empty line between successive methods, please, not an empty line before the }.