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Question about the task

Prices

Java Core, Level 8, Lesson 11

Under discussion

I suppose I've completed all requirements, but it said I didn't re-write the contents. what's wrong? please save me!

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 { if (args.length == 0) {return;} BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String fileName = reader.readLine(); reader.close(); BufferedReader bReader = new BufferedReader(new FileReader(fileName)); FileWriter fileWriter = new FileWriter(fileName, true); int maxId = 0; String line; String product, id, productName, price, quantity; if (args[0].equals("-c")) { while (bReader.ready()) { line = bReader.readLine(); id = line.substring(0, 8).trim(); productName = line.substring(8, 38).trim(); price = line.substring(38, 46).trim(); quantity = line.substring(46, 50).trim(); product = id + productName + price + quantity; fileWriter.write(product +"\n"); int num = Integer.parseInt(id); if(num > maxId) { maxId = num; } } String idNew = String.valueOf(++maxId); String newProduct = String.format("%-8s%-30s%-8s%-4s", idNew, args[1], args[2], args[3]); fileWriter.write(newProduct); } bReader.close(); fileWriter.close(); } }

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Thomas

Level 41 , Bayreuth, Germany

8 December 2022, 11:13

The validator usually does not like file append. So I'd remove that. This will help you get rid of some more problems: You read and write at the same time... (I even didn't know that this is working ;) ) but with that you duplicate entries (cause of append - but you need append otherwise opening the file in write mode will delete the content and you have nothing left to read). So you have to get rid of append. Use a container class (List) or a StringBuilder to collect the data and when reading is done you just save everything in one bunch. Another problem is the id... you properly grab it but after trimming and putting the line together you forgot to add the removed spaces (putting together again isn't necessary - you still have the entire line in a variable). If you eg. use a list products then a PrintWriter would be a nice class to use to write to the file

try (PrintWriter out = new PrintWriter(fileName)) {
    products.forEach(out::println);
}
// alternatively the longer form to write that code
PrintWriter out = new PrintWriter(fileName);
for (String product : products) {
    out.println(product);
}
out.close();

Dawn( #11020889)

Level 37 , Toronto, Canada

9 December 2022, 05:33

many thanks! I still got lost. I need to read more.

Thomas

Level 41 , Bayreuth, Germany

9 December 2022, 07:50

You already have things together. You just need to line all up properly. Write methods for : 1. read the file lines into a List<String> 2. get the last id 3. create a new entry 4. write a List<String> to the file then the code for main is easy (sort of pseudo code but should work this way if you implement the methods)

List<String> products = fileLinesToList(fileName);
int lastId = getLastId(products);
products.add(createNewEntry(lastId++, name, price, count));
saveList(products);