Level 30

Chennai

25.09.2020
490views
8comments

need help

Question about the task

Resolved

Its not test passing the requirements from 3-6 and also i have tried with some inputs in the arguments but it's throwing a StringIndexOutOfBoundsException -c apple 20000 4 but its not working.

CrUD for a table inside a file.
Read a file name for CrUD operations from the console.

The program is started with the following arguments:
-c productName price quantity

Argument values:
where id is 8 characters.
productName is 30 characters.
price is 8 characters.
quantity is 4 characters.
-c adds the product with the specified parameters to the end of the file, and generates an id by incrementing the maximum id found in the file.

The file data is stored in the following order (without separating spaces):
id productName price quantity

Each data field is padded with spaces up to its length.

Before adding a new line, re-write all of its contents to the file.

Example:
19847 Swim trunks, blue 159.00 12 198479 Swim trunks, black with printe173.00 17 19847983Snowboard jacket with reflecti10173.991234

Requirements:

The program should read a file name for CrUD operations from the console.
The Solution class should not use static variables.
When you run the program without arguments, the product list must remain unchanged.
When the program is run with the arguments "-c productName price quantity", a new line with the corresponding product should be added to the end of the file.
The product must have the next id after the maximum id found in the file.
The format of the new product line must precisely match that format specified in the task.
The file streams must be closed.

package com.codegym.task.task18.task1827; /* Prices 1. The program should read a file name for CrUD operations from the console. 2. The Solution class should not use static variables. 3. When you run the program without arguments, the product list must remain unchanged. 4. When the program is run with the arguments "-c productName price quantity", a new line with the corresponding product should be added to the end of the file. 5. The product must have the next id after the maximum id found in the file. 6. The format of the new product line must precisely match that format specified in the task. 7. The file streams must be closed. */ import java.io.*; import java.util.Arrays; import java.util.LinkedList; import java.util.List; public class Solution { public static void main(String[] args) throws Exception { BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); String s = br.readLine(); if(args[0].equals("-c")){ addLine(s,args); } if (args.length==0) return; //if(args.length==0) return; br.close(); } public static void addLine(String filename, String[] arg) throws IOException { BufferedReader br = new BufferedReader(new FileReader(filename)); List<String> list = new LinkedList<>(); while (br.ready()) { String data = br.readLine(); list.add(data); } int id = Integer.parseInt(list.get(list.size()-1).substring(0,8)); String productName = arg[1]; String price = String.valueOf(Double.parseDouble(arg[2])); String quantity = String.valueOf(Integer.parseInt(arg[3])); if (productName.length() < 30) { productName +=" " ; } if (price.length() < 8) { price +=" "; } if (quantity.length() < 4) { quantity +=" "; } byte[] bytes = (id+productName+price+quantity).getBytes(); FileWriter fileWriter = new FileWriter(filename); for (String i : list) { fileWriter.append(i).append("\n"); } fileWriter.write(Arrays.toString(bytes)); br.close(); fileWriter.close(); } }

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Nouser

Level 36 , Germany

25 September 2020, 08:12

useful

- after reading the last id from the file you need to increment it - if the file has no data, you get an exception cause of line 46 trying to get a list element that doesn't exist -> check if list is empty and in that case set the id to 1 else read from list - writing doesn't work cause a) FileWriter takes char arrays or strings. Arrays.toString creates a string that looks similar to [64], [32], [65] and that will be written to the file. So it's from no use to create a string, convert in byte array then call Arrays.toString and save. Just use fileWriter.write(id+productName+price+quantity); Possible additions: - The loops to fill up the spaces work. Also possible would be to use String.format(); Then you have all that loops in one line. - There's also the possiblility, to add the created string to the list and then save the list in a single loop. Either approach is OK, that one looks a little bit cleaner imho.

dhanush

Level 30 , Chennai, India

26 September 2020, 05:51

Thanks bro! I don't know i got correct what you said but i doesn't work it again gives me the same error and it doesn't verify any requirements :(

public static void addLine(String filename, String[] arg) throws IOException {
           BufferedReader br = new BufferedReader(new FileReader(filename));
           List<String> list = new LinkedList<>();

           while (br.ready()) {
               String data = br.readLine();
               list.add(data);
           }
           int id;
           if(list.isEmpty()){
               id=1;
           }else {
               id = Integer.parseInt(list.get(list.size() - 1).substring(0, 8));
               id++;
           }
           String productName = arg[1];
           String price = String.valueOf(Double.parseDouble(arg[2]));
           String quantity = String.valueOf(Integer.parseInt(arg[3]));

           if (productName.length() < 30) {
               productName +=" " ;
           }
           if (price.length() < 8) {
               price +=" ";
           }
           if (quantity.length() < 4) {
               quantity +=" ";
           }
          // byte[] bytes = (id+productName+price+quantity).getBytes();
           FileWriter fileWriter = new FileWriter(filename);
       for (String i : list) {
               fileWriter.append(i).append("\n");
           }

           fileWriter.write(id+productName+price+quantity);
           br.close();
           fileWriter.close();
   }

dhanush

Level 30 , Chennai, India

26 September 2020, 06:14

Also i don't know how the String format works,I think this is how it works?

String lastline = String.format("%-%8d%-%30s%-%8f%-%4d",id,productName,price,quantity);

Nouser

Level 36 , Germany

26 September 2020, 07:49

solution

How String.format() works you can read here % to tell a format command is next - for the alignment eg. 8 for the place used and s for the type that's getting inserted eg. String newString = String.format("%-8s", someString); And I'm not using append but write cause append afaik just takes chars and char sequences. At first I give the args speaking variable names:

String name = args[1];
String price = args[2];
String quantity = args[3];

After list initalization I declare int id = 0; That's for avoiding the if-else check when the list is null. When reading the file I add everything, while reading to the list and grab the max id. If nothing got read, the list is empty and the start id is 0.

BufferedReader br = new BufferedReader(new FileReader(filename));
List<String> list = new LinkedList<>();
int id = 0;

 while (br.ready()) {
     String input = br.readLine();
     list.add(input);

     int tempId = Integer.parseInt(input.substring(0,8).trim());
     id = Math.max(id, tempId);
 }
 br.close();

Now we create the new string from the args, increment the id and add all to the list

list.add(String.format("%-8s%-30s%-8s%-4s", ++id, name, price, quantity));

Last point is, to write everything to the file (using write)

FileWriter fileWriter = new FileWriter(filename);
for (String s : table) fileWriter.write(s + "\n");
fileWriter.close();

I hope I have no typos in it and that it works ;)

dhanush

Level 30 , Chennai, India

26 September 2020, 10:35

Yeah that works bro i got verified but can you give some example how to debug because when test my code donno why but it shows StringIndexOutOfBoundsException when i tested with -c apple 200.00 3 . :(

dhanush

Level 30 , Chennai, India

26 September 2020, 10:41

And also what exactly this line is doing

id = Math.max(id, tempId);

it checks that the last element in the file is maximum or just check the maximum id in the file?

Nouser

Level 36 , Germany

26 September 2020, 12:51

That determins the max id in the file. If you can be sure that it's written in asc or desc order you could grab just the id of the first or last entry. And for debugging I use the IntelliJ built in debugger (there are a few good YouTube videos how to use it) and, if necessary a DEBUG constant and lots of souts ;)

dhanush

Level 30 , Chennai, India

27 September 2020, 16:56

Yeah thanks bro for the clarification. definitely i watch the videos. :)