CodeGym/Help with Java Tasks/Needs come help

Level 24

Amsterdam

15.01.2021
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11comments

Needs come help

Question about the task

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Why do I fail the test? 1) I also do not understand why you can create another CodeGym. You would assume that it should be a singleton? 2) I do not understand why you use codeGym.save(outputStream) what is this suppose to do? I would think that you would save new users to the list that is in the class Codegym But that is not what we're doing? This I find very confusing. 3) Why did we have a lesson on the isPresent boolean to check if a field is blank or not. When are we suppose to use this? 4) What do they mean on line 23 initialize users field for the codeGym object. The only field is the arrayList why would we initialize it here as it is initialized in its own class. So what is the meaning of this?

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.ArrayList; import java.util.Date; import java.util.List; /* 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 { File yourFile = File.createTempFile("task2002", ".txt", new File("/Users/lilianetop/Desktop")); 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 System.out.println(codeGym.equals(loadedObject)); 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 output = new PrintWriter(outputStream); if (!users.isEmpty()) { for (User user : users) { StringBuilder storage = new StringBuilder(); storage.append(user.getFirstName() + "\n"); storage.append(user.getLastName() + "\n"); storage.append(user.getBirthDate() + "\n"); storage.append(user.isMale() + "\n"); storage.append(user.getCountry() + "\n"); output.print(storage.toString()); } } output.close(); } public void load(InputStream inputStream) throws Exception { BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream)); String line = ""; while (reader.ready()) { line = reader.readLine(); String[] fields = line.split("\n"); if (fields.length < 5) { break; } User user = new User(); user.setFirstName(fields[0]); user.setLastName(fields[1]); Date birthDate = new SimpleDateFormat("MM dd yyyy").parse(fields[2]); user.setBirthDate(birthDate); user.setMale(Boolean.parseBoolean(fields[3])); switch (fields[4]) { case "UNITED_STATES": user.setCountry(User.Country.UNITED_STATES); break; case "UNITED_KINGDOM": user.setCountry(User.Country.UNITED_KINGDOM); break; default: user.setCountry(User.Country.OTHER); break; } users.add(user); } reader.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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Guadalupe Gagnon

Level 37 , Tampa, United States

15 January 2021, 16:20

BufferedReaders will only read 1 line at a time, stopping at each line break or the end of the file. This means line 70 will only read the first line (which will be a first name), line 71 will try to split that line into multiple by line breaks (which don't exist since bufferedreader doesn't return any),and line 72 will always be true and the code will break there.

Liliane Top Backend Developer at Procura

15 January 2021, 16:22

something strange is happening as the above is not my code I changed it from"\n" to "/"

public void save(OutputStream outputStream) throws Exception {
            PrintWriter output = new PrintWriter(outputStream);

            if (!this.users.isEmpty()) {
                for (User user : this.users) {
                    StringBuilder storage = new StringBuilder();
                    storage.append(user.getFirstName() + "/");
                    storage.append(user.getLastName() + "/");
                    storage.append(user.getBirthDate() + "/");
                    storage.append(user.isMale() + "/");
                    storage.append(user.getCountry() + "/");

                    output.println(storage.toString());
                }
            }
            output.close();
        }

Liliane Top Backend Developer at Procura

15 January 2021, 16:24

So I read one line which is a user and split it up.

Guadalupe Gagnon

Level 37 , Tampa, United States

15 January 2021, 16:25

useful

Some tips: Line 50: this is not necessary. The foreach loop already has this basic functionality included, it wont enter the loop if the collection is empty. You would need to make this check if you used a for loop. For loops don't pre check this and when the code accessed an index that didn't exist an exception would be thrown That same loop (line 51) You could easily make the StringBuilder before the loop, build the ENTIRE output, then after the loop just output the data in one chunk (less processing time by the CPU this way).

Guadalupe Gagnon

Level 37 , Tampa, United States

15 January 2021, 16:27

useful

I think line breaks are perfect for splitting the data, you just need to make sure that it is: a) written cleanly in an a way that is easily digested by your load algorithm b) and then obviously have a good load algorithm Make sure that, when saved, you do not end with an extra line break or character used to split. That makes reading a lot easier.

Liliane Top Backend Developer at Procura

15 January 2021, 16:36

Line 50 I removed I trim() the line before splitting it but it makes no difference it doesn't save anything..

public void save(OutputStream outputStream) throws Exception {
            PrintWriter output = new PrintWriter(outputStream);
            for (User user : this.users) {
                StringBuilder storage = new StringBuilder();
                storage.append(user.getFirstName() + "/");
                storage.append(user.getLastName() + "/");
                storage.append(user.getBirthDate() + "/");
                storage.append(user.isMale() + "/");
                storage.append(user.getCountry() + "/");

                output.println(storage.toString());

            }
            output.close();
        }

Liliane Top Backend Developer at Procura

15 January 2021, 16:37

public void load(InputStream inputStream) throws Exception {
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
            String line = "";

            while (reader.ready()) {
                line = reader.readLine();
                String[] fields = line.trim().split("/");
                if (fields.length < 5 || fields[0].isEmpty()) break;

                User user = new User();
                user.setFirstName(fields[0]);
                user.setLastName(fields[1]);
                Date birthDate = new SimpleDateFormat("MM dd yyyy").parse(fields[2]);
                user.setBirthDate(birthDate);
                user.setMale(Boolean.parseBoolean(fields[3]));
                switch (fields[4]) {
                    case "UNITED_STATES":
                        user.setCountry(User.Country.UNITED_STATES);
                        break;
                    case "UNITED_KINGDOM":
                        user.setCountry(User.Country.UNITED_KINGDOM);
                        break;
                    default:
                        user.setCountry(User.Country.OTHER);
                        break;
                }
                this.users.add(user);
            }
            reader.close();
        }

Liliane Top Backend Developer at Procura

15 January 2021, 16:39

Also how do I test it. I do not understand why we are trying to save an new instance of CodeGym. I would think that you only want to save users to the ArrayList in the CodeGym class. So what are we doing here:

CodeGym codeGym = new CodeGym();
            // Initialize users field for the codeGym object here //what does this mean?
            codeGym.save(outputStream);
            outputStream.flush();

Guadalupe Gagnon

Level 37 , Tampa, United States

15 January 2021, 17:13

"CodeGym" is the class that contains the List of Users. It is a storage class for users. So you would have your first theoretical CodeGym class with a bunch of users saved. This one would save all the contained users into a file. Next, you create a new CodeGym class and then use that file to fill the list in that with the Users from the first CodeGym object (this is what is going on in the main method). To test this you would have to fill the Users list in the first CodeGym object with data. Just create a method and that adds a bunch of random Users into the List. Here:

// creates 5 randomish users
static void fillData(CodeGym codeGym){
   String[][] names = {"Lucy Bob Katie Ralph Tim".split(" "),
      "Moon Top Gagnon Hastings Nirmul".split(" ")};
   User.Country[] countries = User.Country.values();
   for(int i = 0; i < 5; i++){
      User x = new User();
      x.setBirthDate(new Date());
      x.setCountry(countries[(int)(Math.random()*countries.length)]);
      x.setFirstName(names[0][(int)(Math.random()*names[0].length)]);
      x.setLastName(names[1][(int)(Math.random()*names[1].length)]);
      x.setMale(Math.random()*2 > 1 ? true : false);
      codeGym.users.add(x);
   }
}

Add this method below main, then call it in main on line 23. This will add 5 users. You can add more just by increasing the for loop break point.

Guadalupe Gagnon

Level 37 , Tampa, United States

15 January 2021, 17:18

Some more tips: Since, in the save method, you are writing the date with no special formatting, in the load method you don't need any special formatting either:

// no need to do this, actually this would fail
Date birthDate = new SimpleDateFormat("MM dd yyyy").parse(fields[2]);
user.setBirthDate(birthDate);

// do this instead
user.setBirthDate(new Date(fields[2]));

Also, you can parse enum values:

//So instead of doing this:
switch (fields[4]) {
   case "UNITED_STATES":
      user.setCountry(User.Country.UNITED_STATES);
      break;
   case "UNITED_KINGDOM":
      user.setCountry(User.Country.UNITED_KINGDOM);
      break;
   default:
      user.setCountry(User.Country.OTHER);
      break;
}

// do this:
user.setCountry(User.Country.valueOf(fields[4]));

Nouser

Level 36 , Germany

15 January 2021, 16:18

useful

looking at your code I think your storage object saves 6 lines (5 and a final empty one) when reading the object you read one line and try to split that into 5 parts why not just save 5 lines and when loading read 5 lines (no need for StringBuilder)