What's the problem??

Question about the task

Prices

Java Core, Level 8, Lesson 11

Under discussion

Original:

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

Without using "-c":

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

Using "-c":

String[] args = {"-c","Test using -c","19.00","123"};

19847   Swim trunks, blue             159.00  12
198479  Swim trunks, black with printe173.00  17
19847983Snowboard jacket with reflecti10173.991234
19847984Test using -c                 19.00   123

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 { //lines stores every line in file ArrayList<String> lines = new ArrayList<>(); String fileName = (new BufferedReader(new InputStreamReader(System.in))).readLine(); //Read entire file BufferedReader reader = (new BufferedReader(new FileReader(new File(fileName)))); while (reader.ready()) { lines.add(reader.readLine()); } reader.close(); //If args[0] == "-c", create new line if (args[0].equals("-c")){ //Get lastid String lastline; if (lines.size()>0) lastline = lines.get(lines.size()-1); else lastline = "00000000"; //ids = lastid+1 -> to string -> add spaces String id = String.valueOf(Integer.parseInt(lastline.substring(0,8))+1); String ids = id + (new String(new char[8-id.length()]).replace('\0', ' ')); //Add spaces where needed String product = args[1] + (new String(new char[30-args[1].length()]).replace('\0', ' ')); String price = args[2] + (new String(new char[8-args[2].length()]).replace('\0', ' ')); String quantity = args[3] + (new String(new char[4-args[3].length()]).replace('\0', ' ')); //Add the new line lines.add(ids+product+price+quantity); } //Write to file BufferedWriter writer = (new BufferedWriter(new FileWriter(new File(fileName)))); for (int i=0; i<lines.size(); i++){ writer.write(lines.get(i)); //Call "Enter" to go to new line (I tried without -1 too) if (i<lines.size()-1) writer.write("\n"); } writer.close(); } }

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Earil

Level 25 , Paris, France

4 July 2019, 18:59

useful

First problem with your program is that it assumes that the last ID will also be the maximum one. The conditons don't specify that ("and generates an id by incrementing the maximum id found in the file."). So you need to add that part. Line 30 will throw a number format exception in many cases, because Integer.Parseint can't handle args such as "1234 ". args[1] is ID, not product, args[2] is product, not prices, etc...

Ewerton Backend Developer

4 July 2019, 19:51

1) Hmm... didn't thought of that, I made it observing the example. Now, the new code checks.

19847   Swim trunks, blue             159.00  12
19847983Snowboard jacket with reflecti10173.991234
198479  Swim trunks, black with printe173.00  17
19847984Test using -c                 19.00   123

2) You are right, I thought parseInt would recognize "1234anything" to 1234, as stoi in C++ does. 3) "The program is started with the following arguments: -c productName price quantity" It doesn't give you an ID, so args[1] is really the product, and etc... But, it didn't validate any of the remaining. What suprises me most is the validator n°3.

//Check next id number
ArrayList<Integer> nmids = new ArrayList<>();
for (int i = 0; i < lines.size(); i++) {
    String number = lines.get(i).substring(0,8).replaceAll(" ","");
    nmids.add(Integer.parseInt(number));
}
Collections.sort(nmids);
//If args[0] == "-c", create new line
if (args[0].equals("-c")){
    //Get lastid
    String id = String.valueOf(nmids.get(nmids.size()-1)+1);
    String ids = id + (new String(new char[8-id.length()]).replace('\0', ' '));
    //Add spaces where needed
    String product = args[1] + (new String(new char[30-args[1].length()]).replace('\0', ' '));
    String price = args[2] + (new String(new char[8-args[2].length()]).replace('\0', ' '));
    String quantity = args[3] + (new String(new char[4-args[3].length()]).replace('\0', ' '));
    //Add the new line
    lines.add(ids+product+price+quantity);
}

Earil

Level 25 , Paris, France

5 July 2019, 19:59

useful

Have you tried running it with out arguments ? I think it will throw a IndexOutOfRange exception, because args[0] won't even exist. My working code includes a "if (args.lenght > 0) {all my code}".

Ewerton Backend Developer

5 July 2019, 22:12

Hmm, thank you for the suggestion. Now condition 3 validates.