how and where am I doing wrong?

Question about the task

Prices

Java Core, Level 8, Lesson 11

Resolved

Any help would be great.

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 */ import java.io.*; import java.util.ArrayList; import java.util.Collections; public class Solution { public static void main(String[] args) throws Exception { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String fileName = reader.readLine(); reader.close(); ArrayList<String> idList = new ArrayList<>(); // String argument1 = "-c"; // String argument2 = "something has to be done thd"; // String argument3 = "34.3"; // String argument4 = "342"; // String fileName = "C:/Users/Dan/Desktop/idFile1.txt"; BufferedReader bufferedReader = new BufferedReader(new FileReader(fileName)); while (bufferedReader.ready()) { String idLine = bufferedReader.readLine().substring(0, 8); StringBuffer id = new StringBuffer(); for (int i = 0; i < idLine.length(); i++) { if (!Character.isWhitespace(idLine.charAt(i))) id.append(idLine.charAt(i)); } idList.add(String.valueOf(id)); //adding all ids to the list } bufferedReader.close(); Collections.sort(idList); // sorting the ids System.out.println(idList.toString()); // // //creating a new ID int intId = Integer.parseInt((idList.get(idList.size() - 1))) + 1; String stringId = String.valueOf(intId); while (stringId.length() < 8) { stringId += " "; } System.out.println(stringId); // // //setting product characters length String productName = args[1]; while (productName.length() < 30) { productName += " "; } System.out.println(productName); // // setting price length String price = args[2]; while (price.length() < 8) { price += " "; } System.out.println(price); // //setting quantity length String quantity = args[3]; while (quantity.length() < 4) { quantity += " "; } // System.out.println(quantity); // String productToAdd = stringId + productName + price + quantity; // System.out.println(productToAdd); if (args[0] != null) { FileInputStream inputStream = new FileInputStream(fileName); ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream(); while (inputStream.available() > 0) { byteArrayOutputStream.write(inputStream.read()); } inputStream.close(); FileOutputStream outputStream = new FileOutputStream(fileName); byteArrayOutputStream.writeTo(outputStream); outputStream.write("\n".getBytes()); outputStream.write(productToAdd.getBytes()); outputStream.close(); byteArrayOutputStream.close(); } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

4 January 2021, 20:14

useful

#1 Sorting numbers as Strings wont work for this. Take for example Strings such as: "555" "2222" "6" "11" If these were the id's in the file, the result of line 36 would be: {"11" , "2222", "555", "6"} #2 args won't be null. When a program is started args will populate with the arguments and if no arguments are given then args will be an empty array. This is different than being null. If you the length of an empty array (System.out.println(args.length)) you will get "0", if it were null the program would crash at that point with a NullPointerException. Without going over advanced topics, here are some tips to simplify/improve: - The string class has a .trim() method that removes all leading and trailing whitespace from the String it is called on. Would simplify 27-32 -This code reads from the file twice, once at line 27 and again at line 78. It is good coding practice to never do a task more than once. It is similar to this: you have two tasks, first to organize your green legos and then organize all your legos. If you start off by organizing all your legos to organize the green ones to accomplish the first task (such as getting the id's by reading the whole file), then throw them all over the floor and organize them a second time (to read all the file's content to write).

Chandan Thapa

Level 22 , Dubai, United Arab Emirates

5 January 2021, 15:31

Thanks Guadalupe!! You helped me understand the problem much better. just made two changes : - #1 changed the list to take a Long instead of a String. #2 wrapped my entire code with an if statement by checking the length of args greater than 0. Passed it finally!1 Thanks for your kind help and awesome explanaiton as always. :)

Guadalupe Gagnon

Level 37 , Tampa, United States

5 January 2021, 16:19

useful

Alternatively you can sort numbers as strings, however you have to implement the algorithm as a replacement to the default sort algorithm. Sorting numbers as Strings should first sort by the String length AND THEN if the String lengths are the same, by alphabetical order. Here is a simple description of the algorithm sorting 2 numbers. Just loop it for multiple numbers:

// take 2 Strings that are numbers
String a; String b;
if(b.length > a .length) { // if the length of 'b' is greater than 'a'
   // swap them
} else if(a.length == b.length){ // else if the lengths are the same
   if(b.compareTo(a) > 0) { // AND if 'b' is "greater than" 'a' alphabetically
      // swap them
   }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

5 January 2021, 16:25

useful

Also, I wouldn't recommend wrapping your entire code in an if statement from now on. The purpose of that if statement is to only execute the code if there are args in the array. It would be cleaner to just end the program if there are no args:

if(args.length == 0) return; // this will end the program

// rest of code

instead of doing this:

if(args.length == 0) {
   // rest of code
}

Try to start practicing this: Indent your code as few times as possible. As you learn more about coding you will learn techniques that make accomplishing this much easier... So don't waste too much time now trying to do this 100%. I just offer these as tips.

Chandan Thapa

Level 22 , Dubai, United Arab Emirates

5 January 2021, 17:40

Thanks a ton Guadalupe! this would be very helpful for my further learning as I get deeper into coding and advanced topics. The tips are great! I will follow this as it makes sense not to wrap the entire code in an if statement. Again thanks for the tips and detailed explanations on it. :)