Error in "main"

Hi, I wanna create simple application to manage data for a gameshow. Data is multiple choice question and only question.
I get errors when trying to read data to ArrayList using FileInputStream the second time (the first time is fine).

Code:

---

package QuestionDatabaseManagement;

import java.io.*;
import java.util.*;

public class MultiChoiceQuestion extends Question implements Serializable {

        private static final long serialVersionUID = 4050737259583241901L;
       
        private String OptA, OptB, OptC, OptD;
               
        public String getOptA() {
                return OptA;
        }

        public void setOptA(String optA) {
                if (optA.length()>0)
                        OptA = optA;
        }

        public String getOptB() {
                return OptB;
        }

        public void setOptB(String optB) {
                if (optB.length()>0)
                        OptB = optB;
        }

        public String getOptC() {
                return OptC;
        }

        public void setOptC(String optC) {
                if (optC.length()>0)
                        OptC = optC;
        }

        public String getOptD() {
                return OptD;
        }

        public void setOptD(String optD) {
                if (optD.length()>0)
                        OptD = optD;
        }

        public MultiChoiceQuestion(String ques, String ans, String optA,
                        String optB, String optC, String optD, int type, int dif) {
                super(ques, ans, type, dif);
                OptA = optA;
                OptB = optB;
                OptC = optC;
                OptD = optD;
        }

        public MultiChoiceQuestion() {
                this("","","","","","",0,0);
        }
       
        public void print() {
                System.out.println("Type: " + Category[getType()]);
                System.out.println("Difficulty: " + Dif[getDif()]);
                System.out.println("Question: " + getQues());
                System.out.println("\tA. " + getOptA());
                System.out.println("\tB. " + getOptB());
                System.out.println("\tC. " + getOptC());
                System.out.println("\tD. " + getOptD());
                System.out.println("Answer: " + getAns());
        }
       
        public void input() {
                Scanner Sc = new Scanner(System.in);
                System.out.print("Enter question: ");
                String Q = Sc.nextLine();
                System.out.print("Enter option A: ");
                String Oa = Sc.nextLine();
                System.out.print("Enter option B: ");
                String Ob = Sc.nextLine();
                System.out.print("Enter option C: ");
                String Oc = Sc.nextLine();
                System.out.print("Enter option D: ");
                String Od = Sc.nextLine();
                System.out.print("Enter answer: ");
                String A = Sc.nextLine();
                System.out.print("Enter type: ");
                int T = Sc.nextInt();
                System.out.print("Enter difficulty: ");
                int D = Sc.nextInt();
                setQues(Q);
                setAns(A);
                setOptA(Oa);
                setOptB(Ob);
                setOptC(Oc);
                setOptD(Od);
                setType(T);
                setDif(D);
                Sc.close();
        }
}

---

Code:

---

package QuestionDatabaseManagement;

import java.io.*;
import java.util.*;

public class Question implements Serializable{
       
                private static final long serialVersionUID = -1116686755757636504L;
       
        protected String ques, ans;
        protected int type; //0:NOTSET(only use to initial beginning value)
                                                //1:MATH|2.PHYSICS|3.ENG|4.LITERATURES|5.CHE|6. ASTRO
                                                //7. GEO|8. BIO|9: HIS|10: LAW|11: ARTS&CULTURE
                                                //12.UNDEFINED
        protected String[] Category = {"NOTSET","MATH","PHY","ENG",
                                                                  "LIT","CHE","ASTRO","GEO","BIO","HIS","LAW","ARTS & CULTURE","UNDEFINED"};
        protected int dif; //0: NOTSET
                                          //1: EASY|2: MEDIUM|3: HARD
                                          //4: UNDIFINED
        protected String[] Dif = {"NOTSET","EASY","MEDIUM","HARD","UNDEFINED"};
       
        // The last element of these arrays must always be "UNDEFINED"
        // also the last value of the <type> and <dif> variables should mean "undefined value"
       
        private static int count = 0;

        public String getQues() {
                return ques;
        }

        public void setQues(String ques) {
                this.ques = ques;
        }

        public String getAns() {
                return ans;
        }

        public void setAns(String ans) {
                if (ans.length()>0)
                        this.ans = ans;
        }

        public int getType() {
                return type;
        }
       
        public void setType(int type) {
                if (type>0 && type<Category.length)
                        this.type = type;
                else this.type = Category.length;
        }
       
        public int getCount() {
                return count;
        }

        public int getDif() {
                return dif;
        }

        public void setDif(int dif) {
                this.dif = dif;
        }

        public Question(String ques, String ans, int type, int dif) {
                this.ques = ques;
                this.ans = ans;
                this.type = type;
                this.dif = dif;
                count++;
        }

        public Question() {
                this("","",0,0);
        }
       
        public void print() {
                System.out.println("Type: " + Category[getType()]);
                System.out.println("Dificulty: " + Dif[getDif()]);
                System.out.println("Question: " + getQues());
                System.out.println("Answer: " + getAns());
        }
       
        public void input() {
                Scanner Sc = new Scanner(System.in);
                System.out.println("Enter question: ");
                String Q = Sc.nextLine();
                System.out.println("Enter answer: ");
                String A = Sc.nextLine();
                System.out.println("Enter type: ");
                int T = Sc.nextInt();
                System.out.println("Enter difficulty: ");
                int D = Sc.nextInt();
                setType(T);
                setDif(D);
                setQues(Q);
                setAns(A);
                Sc.close();
        }       
}

---

Code:

---

package QuestionDatabaseManagement;
       
import java.util.*;
import java.io.*;

public class QuestionManagement {

        public static void main(String[] args) throws Exception, IOException, ClassNotFoundException {
               
                ArrayList<MultiChoiceQuestion> MCQ = new ArrayList<MultiChoiceQuestion>();
                ArrayList<Question> Q = new ArrayList<Question>();
               
/*
                FileOutputStream file1 = new FileOutputStream("MCQ.dat");
                FileOutputStream file2 = new FileOutputStream("Q.dat");
               
                MCQ.add(new MultiChoiceQuestion("Bộ phim hoạt hình nổi tiếng Shrek của hãng nào sản xuất?","Walt Disney","Pixar","DreamWorks Animation","Madhouse","C",11,2));
                MCQ.add(new MultiChoiceQuestion("Số tiếp tục trong dãy số dưới đây là số nào?: 6 20 62 188","564","566","568","600","B",1,1));
                MCQ.add(new MultiChoiceQuestion("Nước ở đâu rộng nhất Thế Giới ?","Mỹ","Nga","Trung Quốc","Khác","D",7,1));
                MCQ.add(new MultiChoiceQuestion("Bạn có biết có khoảng bao nhiêu ngôn ngữ có trên trái đất?","3500","4700","6500","7300","C",11,2));
                MCQ.add(new MultiChoiceQuestion("Trong 4 con vật sau đây, thì con nào có đặc điểm ít giống nhất với 3 con còn lại?","Chó","Voi","Mèo","Rùa","D",8,1));
                ObjectOutputStream out1 = new ObjectOutputStream(file1);
                out1.writeObject(MCQ);
                out1.close();
               
                Q.add(new Question("Sông nào có một bờ ở châu Âu, một bờ ở châu Á?","Sông U-ran",7,2));
                Q.add(new Question("Hành tinh nào lớn nhất trong hệ Mặt Trời?","Mộc tinh",6,1));
                Q.add(new Question("Trong bức tranh Đám cưới chuột có tất cả bao nhiêu con chuột?","12",3,3));
                Q.add(new Question("Đồng bằng nào lớn nhất thế giới?","Amazon",4,4));
                Q.add(new Question("Chữ cái cuối cùng trong bảng chữ cái Hy Lạp?","Omega",5,0));
                ObjectOutputStream out2 = new ObjectOutputStream(file2);
                out2.writeObject(Q);
                out2.close();
*/
                FileInputStream file1 = new FileInputStream("MCQ.dat");
                ObjectInputStream in1 = new ObjectInputStream(file1);
                MCQ = (ArrayList)in1.readObject();
                in1.close();
                FileInputStream file2 = new FileInputStream("Q.dat");
                ObjectInputStream in2 = new ObjectInputStream(file2);
                Q = (ArrayList)in2.readObject();
                in2.close();

                byte selection;
                do {
                        Scanner Sc = new Scanner(System.in);
                        System.out.println("Please select one: ");
                        System.out.println("\t1. Add a muiltiple choice question");
                        System.out.println("\t2. Add a question");
                        System.out.println("\t3. Delete a multiple choice question");
                        System.out.println("\t4. Delete a question");
                        System.out.println("\t6. Edit a multiple choice question");
                        System.out.println("\t6. Edit a question");
                        System.out.println("\t7. Report: Multiple choice question database");
                        System.out.println("\t8. Report: Question database");
                        System.out.println("\t9. Report: All database");
                        System.out.println("Enter your choice: ");
                        selection = Sc.nextByte();

                        switch (selection) {
                                case 1:
                                        MultiChoiceQuestion M = new MultiChoiceQuestion();
                                        M.input();
                                        MCQ.add(M);
                                        break;
                                case 2:
                                        Question Que = new Question();
                                        Que.input();
                                        Q.add(Que);
                                        break;
                                case 3:
                                       
                                case 4:
                                        break;
                                case 5:
                                        break;
                                case 6:
                                        for (int i = 0; i < MCQ.size(); i++) MCQ.get(i).print();
                                        break;
                                case 7:
                                        for (int i = 0; i < Q.size(); i++) Q.get(i).print();
                                        break;
                                case 8:
                                        break;
                                default: break;
                        }
                }
                while (selection>0 && selection<7);
        }
}

---

Error here

Code:

---

Please select one:
        1. Add a muiltiple choice question
        2. Add a question
        3. Delete a multiple choice question
        4. Delete a question
        6. Edit a multiple choice question
        6. Edit a question
        7. Report: Multiple choice question database
        8. Report: Question database
        9. Report: All database
Enter your choice:
1
Enter question: 1
Enter option A: 1
Enter option B: 1
Enter option C: 1
Enter option D: 1
Enter answer: 1
Enter type: 1
Enter difficulty: 1
Please select one:
        1. Add a muiltiple choice question
        2. Add a question
        3. Delete a multiple choice question
        4. Delete a question
        6. Edit a multiple choice question
        6. Edit a question
        7. Report: Multiple choice question database
        8. Report: Question database
        9. Report: All database
Enter your choice:
Exception in thread "main" java.util.NoSuchElementException
        at java.util.Scanner.throwFor(Scanner.java:907)
        at java.util.Scanner.next(Scanner.java:1530)
        at java.util.Scanner.nextByte(Scanner.java:1924)
        at java.util.Scanner.nextByte(Scanner.java:1883)
        at QuestionDatabaseManagement.QuestionManagement.main(QuestionManagement.java:58)

---

Please help me :). Thanks

Looks like you wrote out the object with one version of the class and are reading in with another?

The class that is serialized doesn't equal the serial of the local class.

This is mainly because you didn't add your own serial for the class so Java hashes most of your functions and creates a serial out of that, so if you change even the slightest detail, the serial will change and will not match. The serial will also differ from compiler to compiler, so it's highly recommended to add your own serial, instead of letting the compiler make one for you.

Add serials to your class, the class you're getting an error with should have a serial of: 8116156216592075411

Quote:

---

Originally Posted by Tolls

Looks like you wrote out the object with one version of the class and are reading in with another?

---

I wrote some samples first then read them into ArrayList. The first time reading is OK, but the second time I run the program, these errors appeared. Also, I'm learning how to write and read file, so if there are anything wrong, please teach me :)

Quote:

---

Originally Posted by JBelg

The class that is serialized doesn't equal the serial of the local class.

This is mainly because you didn't add your own serial for the class so Java hashes most of your functions and creates a serial out of that, so if you change even the slightest detail, the serial will change and will not match. The serial will also differ from compiler to compiler, so it's highly recommended to add your own serial, instead of letting the compiler make one for you.

Add serials to your class, the class you're getting an error with should have a serial of: 8116156216592075411

---

Hmm, in my teacher presentation slide, she doesn't add the serial. Let me try it then I will report.

OK, updated CODE, so there is an error with the input. Please help me on this error and explain please cause I faced this error so many times, fixed with lucky but don't know how I fix it. Thanks

Please don't change the original post like that.
It makes large chunks of the thread nonsensical.

Ah yes, sorry :), just want to make the thread clean. So, do you know what is my fault?

You've got multiple Scanners reading the Sys.in stream.
Now, I haven't gone through your code, but it's quite possible that they are clashing.
Scanner has a buffer, and if one Scanner has consumed the data before the one you really want to consume the data then you might hit problems.
This is likely to be a bit random as well.

Quote:

---

Originally Posted by Tolls

You've got multiple Scanners reading the Sys.in stream.
Now, I haven't gone through your code, but it's quite possible that they are clashing.
Scanner has a buffer, and if one Scanner has consumed the data before the one you really want to consume the data then you might hit problems.
This is likely to be a bit random as well.

---

Yes, I know this problem too, but I don't know how to fix it after although send the Sc.next() or Sc.nextLine()

I was going to suggest trying to close each of them when finished, but you seem to have done that...apart from the one in main().
I'd close that one as well.

The other option is to have a single Scanner that you access.

Hmm, so can you tell me what is the solution for my case cause I don't know how to fix it in the past, just lucky

Close the Scanner.
You;re doing it everywhere else except in main().
Once you have the 'selection' you may as well call close() on the scanner object.

Can't solve by closing Scanner too. I even close Scanner each case but it does not seem to be fixed.

Code:

---

package QuestionDatabaseManagement;

import java.util.*;
import java.io.*;
 
public class QuestionManagement {
 
    public static void main(String[] args) throws IOException, ClassNotFoundException {
       
        ArrayList<MultiChoiceQuestion> MCQ = new ArrayList<MultiChoiceQuestion>();
        ArrayList<Question> Q = new ArrayList<Question>();
       
/*
        FileOutputStream file1 = new FileOutputStream("MCQ.dat");
        FileOutputStream file2 = new FileOutputStream("Q.dat");
       
        MCQ.add(new MultiChoiceQuestion("Bộ phim hoạt hình nổi tiếng Shrek của hãng nào sản xuất?","Walt Disney","Pixar","DreamWorks Animation","Madhouse","C",11,2));
        MCQ.add(new MultiChoiceQuestion("Số tiếp tục trong dãy số dưới đây là số nào?: 6 20 62 188","564","566","568","600","B",1,1));
        MCQ.add(new MultiChoiceQuestion("Nước ở đâu rộng nhất Thế Giới ?","Mỹ","Nga","Trung Quốc","Khác","D",7,1));
        MCQ.add(new MultiChoiceQuestion("Bạn có biết có khoảng bao nhiêu ngôn ngữ có trên trái đất?","3500","4700","6500","7300","C",11,2));
        MCQ.add(new MultiChoiceQuestion("Trong 4 con vật sau đây, thì con nào có đặc điểm ít giống nhất với 3 con còn lại?","Chó","Voi","Mèo","Rùa","D",8,1));
        ObjectOutputStream out1 = new ObjectOutputStream(file1);
        out1.writeObject(MCQ);
        out1.close();
       
        Q.add(new Question("Sông nào có một bờ ở châu Âu, một bờ ở châu Á?","Sông U-ran",7,2));
        Q.add(new Question("Hành tinh nào lớn nhất trong hệ Mặt Trời?","Mộc tinh",6,1));
        Q.add(new Question("Trong bức tranh Đám cưới chuột có tất cả bao nhiêu con chuột?","12",3,3));
        Q.add(new Question("Đồng bằng nào lớn nhất thế giới?","Amazon",4,4));
        Q.add(new Question("Chữ cái cuối cùng trong bảng chữ cái Hy Lạp?","Omega",5,0));
        ObjectOutputStream out2 = new ObjectOutputStream(file2);
        out2.writeObject(Q);
        out2.close();
*/

        FileInputStream file1 = new FileInputStream("MCQ.dat");
        ObjectInputStream in1 = new ObjectInputStream(file1);
        MCQ = (ArrayList)in1.readObject();
        in1.close();
        FileInputStream file2 = new FileInputStream("Q.dat");
        ObjectInputStream in2 = new ObjectInputStream(file2);
        Q = (ArrayList)in2.readObject();
        in2.close();

        int s, s1;
        do {
                Scanner Sc = new Scanner(System.in);
                System.out.println("***************************************************************************************");
            System.out.println("Please select one: ");
            System.out.println("\t1. Add a multiple choice question");
            System.out.println("\t2. Add a question");
            System.out.println("\t3. Delete a multiple choice question");
            System.out.println("\t4. Delete a question");
            System.out.println("\t5. Edit a multiple choice question");
            System.out.println("\t6. Edit a question");
            System.out.println("\t7. Report: Multiple choice question database");
            System.out.println("\t8. Report: Question database");
            System.out.println("\t9. Report: All database");
            System.out.print("Enter your choice: ");
            s = Sc.nextInt();
            System.out.println("***************************************************************************************");
            switch (s) {
                    case 1:
                            MultiChoiceQuestion M = new MultiChoiceQuestion();
                    M.input();
                    MCQ.add(M);
                    Sc.close();
                    break;
                case 2:
                    Question Que = new Question();
                    Que.input();
                    Q.add(Que);
                    Sc.close();
                    break;
                case 3:
                        Sc.close();
                    break;
                case 4:
                        Sc.close();
                    break;
                case 5:
                        Sc.close();
                        break;
                case 6:
                        Sc.close();
                        break;
                case 7:
                    for (int i = 0; i < MCQ.size(); i++) MCQ.get(i).print();
                    Sc.close();
                    break;
                case 8:
                    for (int i = 0; i < Q.size(); i++) Q.get(i).print();
                    Sc.close();
                    break;
                case 9:
                        Sc.close();
                    break;
                default: break;
            }
          Sc.close();
        }
        while (s>0 && s<10);
    }
}

---

Code:

---

Exception in thread "main" java.util.NoSuchElementException
        at java.util.Scanner.throwFor(Scanner.java:907)
        at java.util.Scanner.next(Scanner.java:1530)
        at java.util.Scanner.nextInt(Scanner.java:2160)
        at java.util.Scanner.nextInt(Scanner.java:2119)
        at QuestionDatabaseManagement.QuestionManagement.main(QuestionManagement.java:60)

---

No, close it as soon as you have that int.

Code:

---

s = Sc.getInt();
Sc.close();
switch (s) etc etc

---

So after close it, I face error in the MultiChoiceQuestion class

Code:

---

  public void input() {
        Scanner Sc = new Scanner(System.in);
        System.out.print("Enter question: ");
        String Q = Sc.nextLine();
        [B][I][U]System.out.print("Enter option A: ");[/U][/I][/B]
        String Oa = Sc.nextLine();
        System.out.print("Enter option B: ");
        String Ob = Sc.nextLine();
        System.out.print("Enter option C: ");
        String Oc = Sc.nextLine();
        System.out.print("Enter option D: ");
        String Od = Sc.nextLine();
        System.out.print("Enter answer: ");
        String A = Sc.nextLine();
        System.out.print("Enter type: ");
        int T = Sc.nextInt();
        System.out.print("Enter difficulty: ");
        int D = Sc.nextInt();
        setQues(Q);
        setAns(A);
        setOptA(Oa);
        setOptB(Ob);
        setOptC(Oc);
        setOptD(Od);
        setType(T);
        setDif(D);
        Sc.close();
    }

---

Code:

---

Exception in thread "main" java.util.NoSuchElementException: No line found
        at java.util.Scanner.nextLine(Unknown Source)
        at Assignment.MultiChoiceQuestion.input(MultiChoiceQuestion.java:79)
        at Assignment.QuestionManagement.main(QuestionManagement.java:66)

---

Haha, this drives me crazy....

P/S: if you use TeamViewer, please consider pm me through Yahoo silveraero_light at 9 to 10 o'clock GMT+7 and teach me about this issue :D