CodeGym/Help with Java Tasks/Help is appreciated

Level 22

19.10.2020
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8comments

Help is appreciated

Question about the task

Prices

Java Core, Level 8, Lesson 11

Resolved

I did a few tests and it seems to be working fine but it fails one of the tests..

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; public class Solution { public static void main(String[] args) throws Exception { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); if ((args.length > 1) && args[0].equals("-c")) { String fileName = reader.readLine(); addProduct(fileName, args[1], args[2], args[3]); } } public static void addProduct(String fileName, String productName, String price, String quantity) throws IOException { FileOutputStream outputStream = new FileOutputStream(fileName, true); String id = getId(fileName); StringBuilder idStr = new StringBuilder(getId(fileName)); StringBuilder productStr = new StringBuilder(productName); StringBuilder priceStr = new StringBuilder(price); StringBuilder quantityStr = new StringBuilder(quantity); if (id.length() < 8) { for (int i = id.length(); i < 8; i++) { idStr.append(" "); } } else idStr.setLength(8); if (productName.length() < 30) { for (int i = productName.length(); i < 30; i++) { productStr.append(" "); } } else productStr.setLength(30); if (price.length() < 8) { for (int i = price.length(); i < 8; i++) { priceStr.append(" "); } } priceStr.setLength(8); if (quantity.length() < 4) { for (int i = quantity.length(); i < 4; i++) { quantityStr.append(" "); } }quantityStr.setLength(4); String productLine = idStr.toString() + productStr.toString() + priceStr.toString() + quantityStr.toString(); outputStream.write(productLine.getBytes()); outputStream.close(); } public static String getId(String fileName) throws IOException { int id = 1; FileInputStream inputStream = new FileInputStream(fileName); BufferedReader lineReader = new BufferedReader(new InputStreamReader(inputStream)); ArrayList<String> lines = new ArrayList<>(); String data; while ((data = lineReader.readLine()) != null) { lines.add(data); } lineReader.close(); inputStream.close(); if (!lines.isEmpty()) { id = Integer.parseInt(lines.get(lines.size()-1).substring(0, 8).trim()) + 1; return String.valueOf(id); } return String.valueOf(id); } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

19 October 2020, 21:00

I haven't had a chance to test the code, and probably wont be able to tonight, but I think the problem may be the last line of the conditions: "Before adding a new line, re-write all of its contents to the file." Try changing line 24 to:

FileOutputStream outputStream = new FileOutputStream(fileName); // remove true

Then you need to modify the code a bit so that each line read in is subsequently written to the file.

Seferi

Level 22 , United Federation of Planets

20 October 2020, 11:32

Thanks for the reply mate, I somehow missed the last line of the conditions... :/ I refactored the code with changes to re-write the contents first. Also stole some regex from one of your replies and added that too. Now it fails 3 conditions... 🤯 The problem is It's appending on the same line..

public static void addProduct(String fileName, String productName, String price, String quantity) throws IOException {
        FileInputStream inputStream = new FileInputStream(fileName);
        String id = getId(fileName);
        byte[] buffer = new byte[inputStream.available()];
        while (inputStream.available() > 0) {
            inputStream.read(buffer);
        }
        inputStream.close();
        FileOutputStream outputStream = new FileOutputStream(fileName);
        FileOutputStream appendStream = new FileOutputStream(fileName, true);

        outputStream.write(buffer);
        appendStream.write(String.format("%-8s%-30s%-8s%-4s",id,productName,price, quantity).getBytes());
        outputStream.close();
        appendStream.close();
}

Guadalupe Gagnon

Level 37 , Tampa, United States

20 October 2020, 13:11

solution

try:

public static void addProduct(String fileName, String productName, String price, String quantity)
throws IOException {
        FileInputStream inputStream = new FileInputStream(fileName);
        String id = getId(fileName);
        byte[] buffer = new byte[inputStream.available()];
        while (inputStream.available() > 0) {
            inputStream.read(buffer);
        }
        inputStream.close();
        FileOutputStream outputStream = new FileOutputStream(fileName);
        //FileOutputStream appendStream = new FileOutputStream(fileName, true);

        outputStream.write(buffer);
        //write to first outputStream, also add a new line character (\n) before the new product
        outputStream.write(String.format("\n%-8s%-30s%-8s%-4s",id,productName,price, quantity).getBytes());
        outputStream.close();
        //appendStream.close();
}

Nouser

Level 36 , Germany

20 October 2020, 14:31

just an idea... cause you already read the file into a list. Attach the args to the list of parameters (getId method). Then add the new product to the list and let the method return the array.

lines.add(String.format("%-8s%-30s%-8s%-4s", id, all_the_other_data);

In the main just loop through the array and write line by line (with adding linebreaks).

outputStream.write(line + "\n");

Seferi

Level 22 , United Federation of Planets

20 October 2020, 15:18

@Guadalupe This worked mate but I have a question. We write the buffer on line 13, isn't line 15 then overwrite everything because we don't have the append "true" on line 10 ?

Seferi

Level 22 , United Federation of Planets

20 October 2020, 15:58

Good idea mate. I thought of doing that in the beginning but I'm trying to divide the jobs to small pieces to have reusable methods.. Not sure if I'm doing it right or overdo..

Guadalupe Gagnon

Level 37 , Tampa, United States

20 October 2020, 16:21

"We write the buffer on line 13, isn't line 15 then overwrite everything because we don't have the append "true" on line 10 ? " - nope. OutputStreams continue writing from where they last left off (when using the same object that is). Because you are using the same Outputstream object it writes it in the order you specify (line 13 first then line 15). You probably haven't realized this yet, but "System.out" is a PrintStream (which is a type of OutputStream like FileOutputStream) that you use to write to the console using commonly the .print() or .println() methods. It works the same exact way in that it prints from the last point left off at instead of over writing the last thing written to the screen.

Seferi

Level 22 , United Federation of Planets

20 October 2020, 18:32

That cleared it up. Thanks mate.