CodeGym/Help with Java Tasks/need help

Level 30

Chennai

11.09.2020
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13comments

need help

Question about the task

Reading and writing to a file: CodeGym

Java Core, Level 10, Lesson 2

Resolved

Second requirement is not satisfying. :(

Implement the logic for file IO for the CodeGym class.
The file your_file_name.tmp can contain several CodeGym objects.
The main method exists just for you and is not involved in testing the solution.

Requirements:

The read/write logic in the save/load methods must work correctly when the users list is empty.
The read/write logic in the save/load methods must work correctly when the users list is not empty.
The Solution.CodeGym class should not support the Serializable interface.
The Solution.CodeGym class must be public.
The Solution.CodeGym class should not support the Externalizable interface.

package com.codegym.task.task20.task2002; import java.io.*; import java.text.SimpleDateFormat; import java.util.*; /* Reading and writing to a file: CodeGym */ public class Solution { public static void main(String[] args) { // You can find your_file_name.tmp in your TMP directory or adjust outputStream/inputStream according to your file's actual location try { //BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); //String yourFile = br.readLine(); File yourFile = File.createTempFile("your_file_name", null); OutputStream outputStream = new FileOutputStream(yourFile); InputStream inputStream = new FileInputStream(yourFile); CodeGym codeGym = new CodeGym(); // Initialize users field for the codeGym object here codeGym.save(outputStream); outputStream.flush(); CodeGym loadedObject = new CodeGym(); loadedObject.load(inputStream); // Here check that the codeGym object is equal to the loadedObject object outputStream.close(); inputStream.close(); } catch (IOException e) { //e.printStackTrace(); System.out.println("Oops, something is wrong with my file"); } catch (Exception e) { //e.printStackTrace(); System.out.println("Oops, something is wrong with the save/load method"); } } public static class CodeGym { public List<User> users = new ArrayList<>(); public void save(OutputStream outputStream) throws Exception { PrintWriter writer = new PrintWriter(outputStream);// Implement this method String isUser = !users.isEmpty()?"Yes":"No"; writer.println(isUser); writer.println(users); writer.flush(); if(!users.isEmpty()){ for (User s : users){ String firstname = s.getFirstName(); String lastname = s.getLastName(); String date = s.getBirthDate().toString(); String male = s.isMale()?"Yes":"No"; String country = s.getCountry().toString(); writer.println(firstname+","+lastname+","+date+","+male+","+country); for(int i=0; i<users.size(); i++){ s=users.get(i); firstname = s.getFirstName(); lastname = s.getLastName(); date = s.getBirthDate().toString(); male = s.isMale()?"Yes":"No"; country = s.getCountry().toString(); writer.println("\n"+firstname+ "," + lastname+ "," + date+ "," +male+ "," +country); } } } writer.flush(); writer.close(); } public void load(InputStream inputStream) throws Exception { Scanner scan = new Scanner(inputStream);// Implement this method String isUser = scan.nextLine(); if(isUser!=null){ if(users.isEmpty()){ if(isUser.equals("Yes")){ User user = new User(); if(scan.nextLine().equals("true")){ user.setFirstName(scan.nextLine()); } if(scan.nextLine().equals("true")){ user.setLastName(scan.nextLine()); } if(scan.nextLine().equals("true")){ SimpleDateFormat date = new SimpleDateFormat("MM dd yyyy"); Date d = date.parse(scan.nextLine()); user.setBirthDate(d); } if(scan.nextLine().equals("ture")){ user.setMale(true); }else { user.setMale(false); } if(isUser.equals(User.Country.UNITED_STATES)){ user.setCountry(User.Country.UNITED_STATES); }else if(isUser.equals(User.Country.UNITED_KINGDOM)){ user.setCountry(User.Country.UNITED_KINGDOM); }else{ user.setCountry(User.Country.OTHER); } users.add(user); } } } scan.close(); } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; CodeGym codeGym = (CodeGym) o; return users != null ? users.equals(codeGym.users) : codeGym.users == null; } @Override public int hashCode() { return users != null ? users.hashCode() : 0; } } }

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Nouser

Level 36 , Germany

11 September 2020, 07:09

You're checking to much and you're doing to much not necessary stuff. - line 82 is probably not wanted. If you have a user list and want to load an older version then you do not allow that - lines like 86... where do you get that true 'from'? - all the 'Yes/ No' strigs you do not need. isMale is a bolean. If you save it, it reads true/ false. The users... imagine a file where all useres are saved to (or none, if the list is empty). And imagine a BufferedReader... then we check if we have to read something... if (reader.ready()) -> the user list isn't empty. And we have save a fixed amount of lines for each user (5). So if we read these 5 lines in a loop and check if there is a next line, then we know we need to continue... like while(reader.ready()) {user.add(firstName, lastName...);} That's the entire code necesary ;) And saving is more than easy cause you just need to save in a for each loop all data you have with just one check: if (!users.isEmpty())

dhanush

Level 30 , Chennai, India

11 September 2020, 09:15

Thank you Nouser! I tried what you recommended but now it's showing that check why an exception occurs in save/load method but i not getting any exception.

Nouser

Level 36 , Germany

11 September 2020, 11:04

code? oops means an exception

dhanush

Level 30 , Chennai, India

11 September 2020, 11:53

Oh yeah forgot to send

public void save(OutputStream outputStream) throws Exception {
            PrintWriter writer = new PrintWriter(outputStream);// Implement this method

            String isUser = !users.isEmpty()?"Yes":"No";
            writer.println(isUser);
            writer.println(users);
            writer.flush();

            if(!users.isEmpty()){
                for (User s : users){
                    String firstname = s.getFirstName();
                    String lastname = s.getLastName();
                    String date = s.getBirthDate().toString();
                    String male = s.isMale()?"Yes":"No";
                    String  country = s.getCountry().toString();
                    writer.write(firstname);
                    writer.write(lastname);
                    writer.write(date);
                    writer.write(male);
                    writer.write(country);

                    /*for(int i=0; i<users.size(); i++){
                         s=users.get(i);
                    firstname = s.getFirstName();
                    lastname = s.getLastName();
                    date = s.getBirthDate().toString();
                    male = s.isMale()?"Yes":"No";
                    country = s.getCountry().toString();
                        writer.println("\n"+firstname+ "," + lastname+ "," + date+ "," +male+ "," +country);
                    }*/
                }
            }
            writer.flush();
            writer.close();
        }

dhanush

Level 30 , Chennai, India

11 September 2020, 11:54

public void load(InputStream inputStream) throws Exception {
           Scanner scan = new Scanner(inputStream);// Implement this method

           if(scan.hasNext()){
                String isUser = scan.nextLine();
               if(isUser.equals("Yes")){
                   User user = new User();

                   user.setFirstName(scan.nextLine());

                   user.setLastName(scan.nextLine());

                   SimpleDateFormat date = new SimpleDateFormat("MM dd yyyy");
                   Date d = date.parse(scan.nextLine());
                   user.setBirthDate(d);

                   Boolean male = Boolean.parseBoolean(scan.nextLine());
                   user.setMale(male);

               if(isUser.equals(User.Country.UNITED_STATES)){
                   user.setCountry(User.Country.UNITED_STATES);
               }else
               if(isUser.equals(User.Country.UNITED_KINGDOM)){
                   user.setCountry(User.Country.UNITED_KINGDOM);
               }else{
                   user.setCountry(User.Country.OTHER);
               }
                   users.add(user);
           }
       }
           scan.close();
   }

Nouser

Level 36 , Germany

11 September 2020, 12:06

solution

that's not exactly what I meant

public void save(OutputStream outputStream) throws Exception {
    PrintWriter writer = new PrintWriter(outputStream);
    if (!users.isEmpty()) {
        for (User u : users) {
            writer.println(u.getFirstName());
            .....
        }
    }
    writer.flush();
}

and

public void load(InputStream inputStream) throws Exception {
    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
    while (reader.ready()) {
            User user = new User();
            user.setFirstName(reader.readLine());
            ....
            users.add(user);
    }
}

or you add a constructor to the Uset class and do something like that:

while (reader.ready()) {
        users.add( new User(reader.readLine(), /* firstName*/
                            reader.readLine(), /* lastName */
                            .....

everything straight forward, no if else clauses

Nouser

Level 36 , Germany

11 September 2020, 12:11

Oh.. and the exception problem may be the use of the Scanner class as it handles exceptions by itself

Nouser

Level 36 , Germany

11 September 2020, 12:22

and you can try: writer.println(u.getBirthDate().getTime()); vs new Date(Long.parseLong(reader.readLine())) writer.println(u.getCountry()); vs User.Country.valueOf(reader.readLine())

dhanush

Level 30 , Chennai, India

11 September 2020, 13:31

You nailed it bro! This really make me crazy, don't know exactly what i'm doing and checked how to do in other helps comment, in that i checked gagnon's comment which is somewhat similar to mine in that he said that everything should be printed in new line and gave an example code i just followed that but can't able to think what's going on then i came to post mine for help. how did you tested my code because it doesn't suitable for testing when i ran the code it show's the result that your code ran without any error that's it, how to test this code?

Nouser

Level 36 , Germany

11 September 2020, 13:46

specify the save path of the tmp file so you easily can have a look at it

File yourFile = File.createTempFile("task2002", ".txt", new File("C:/Temp/"));

fill the list with some data (with an added constructor in the User class, see above)

SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy");
codeGym.users.add(new User("a", "A", sdf.parse("01-01-2001"), true, User.Country.OTHER));
codeGym.users.add(new User("b", "B", sdf.parse("02-02-2002"), false, User.Country.UNITED_KINGDOM));

now you're ready to debug your code

dhanush

Level 30 , Chennai, India

11 September 2020, 13:52

Yeah i tried with that it works. And the exception i asked occurs in between the lines 48-51 actually don't know why but when i first ran my code it shows the error message that Oops, something is wrong with the save/load method i think the line 28 checks the user is check it not null and the line 50 prints the user and what if the user is null may be this could be error i think so. when i use Scanner it works fine. Even i also tried with BufferedReader Cool! :)

Nouser

Level 36 , Germany

11 September 2020, 14:10

When you use Scanner it won't throw an IOException as the Scanner class itself handles these. To get them you need to call a method, ioException() So this task is probably meant to use BufferedReader. Otherwise catching IOExceptions makes no sense and you won't see them even if they occur. And have you checked how line 50 looks within the saved file? Cause this makes no sense. You try to write the list using println and then 3 lines below you try it by looping through the list and writing each element separately.

dhanush

Level 30 , Chennai, India

11 September 2020, 14:25

Yeah you were right the line 50 makes no sense. That means it won't throw the IOException even if we try to throws the exception it just handles the situation by itself. Nice thanks for that.