CodeGym/Help with Java Tasks/Please help

Level 30

London

20.01.2020
829views
17comments

Please help

Question about the task

Prices

Java Core, Level 8, Lesson 11

Resolved

I changed lines 19-35 to:

String productID = "";
        String productName = reader.readLine();
        String productPrice = reader.readLine();
        String productQuantity = reader.readLine();

        String product = "";

            productID = getID(fileName);
            productName = fullName(productName);
            productPrice = fullPrice(productPrice);
            productQuantity = fullQuantity(productQuantity);
            product = productID + productName + productPrice + productQuantity;

            writer.write("\n" + product);

in order to test the code and used the following input: C:\Users\User\Products.txt swimming trunks 150.00 5 and the program threw a NullPointerException

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(); FileOutputStream fileOutputStream = new FileOutputStream(fileName, true); BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(fileOutputStream)); String productID = ""; String productName = ""; String productPrice = ""; String productQuantity = ""; String product = ""; if (args[0].equals("-c")){ productID = getID(fileName); productName = fullName(args[1]); productPrice = fullPrice(args[2]); productQuantity = fullQuantity(args[3]); product = productID + productName + productPrice + productQuantity; writer.write("\n" + product); } reader.close(); fileOutputStream.close(); writer.close(); } //get ID public static String getID(String fileName) throws Exception { ArrayList<String> products = allProducts(fileName); ArrayList<Integer> productIDs = productIDs(products); int id = productIDs.get(productIDs.size()-1) +1; return fullID(id); } //return sorted ArrayList of product IDs public static ArrayList<Integer> productIDs(ArrayList<String> list) { ArrayList<Integer> productIDs = new ArrayList<>(); for (String string : list){ productIDs.add(getProductID(string)); } Collections.sort(productIDs); return productIDs; } //get the ID of a product public static int getProductID(String product){ String productIDString = product.substring(0, 7); int productID = Integer.parseInt(productIDString.replaceAll(" ", "")); return productID; } // return ArrayList of all products in the file public static ArrayList<String> allProducts(String fileName) throws Exception{ BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(fileName))); ArrayList<String> products = new ArrayList<>(); String s; while (!(s = reader.readLine()).equals(null)){ products.add(s); } reader.close(); return products; } //make sure ID is 8 characters long public static String fullID(int id){ StringBuilder idAsString = new StringBuilder(String.valueOf(id)); while (idAsString.length()!=8){ idAsString.append(" "); } return idAsString.toString(); } //make sure product name is 30 characters long public static String fullName(String name){ StringBuilder fullName = new StringBuilder(name); while (fullName.length()!=30){ fullName.append(" "); } return fullName.toString(); } //make sure price is 8 characters long public static String fullPrice(String s){ StringBuilder price = new StringBuilder(s); while (price.length()!=8){ price.append(" "); } return price.toString(); } //make sure quantity is 4 characters long public static String fullQuantity(String s){ StringBuilder quantity = new StringBuilder(s); while (quantity.length()!=4){ quantity.append(" "); } return quantity.toString(); } }

Comments (17)

Popular
New
Old

You must be signed in to leave a comment

Guadalupe Gagnon

Level 37 , Tampa, United States

20 January 2020, 14:50

useful

Try changing line 70 to:

while ((s = reader.readLine()) != null ){

When objects are null you will not be able to use a method on them (like the .equals()). Remember this because you will see testing for null values before methods are called in code sort of like this:

if(Object != null && Object.someMethod());

or if not a boolean

if(Object != null)
   Object.someMethod();

In this bit of code, if object is null then .someMethod() will never be called (and a null pointer exception thrown). It is a handy little check.

Anthony Chalk

Level 30 , London, United Kingdom

20 January 2020, 14:56

Thank you. However, it's still not passing conditions 3, 5, and 6

Guadalupe Gagnon

Level 37 , Tampa, United States

20 January 2020, 15:14

Couple things to try: - The product ID's may not be in order, try sorting them before adding one. - Also, if I remember correctly, this task does not like appends of the file. Try to write all the original data back to the file before adding the new line. You could accomplish this without too much of a headache by creating an ArrayList that calls allProducts, then passing that to getID:

psvm(){ // main method
   //...
   ArrayList<String> fileData = allProducts(fileName);
   productID = getID(fileData);
   //...
}

public static String getID(ArrayList<String> products) throws Exception {
   ArrayList<Integer> productIDs = productIDs(products);
   int id = productIDs.get(productIDs.size()-1) +1;
   return fullID(id);
}

Now you have the products to write back to the file, in main, which you can do first. A thought, you don't need to do this but I think it makes sense. Your 4 methods that start with 'full' (like fullID, fullName, etc), you could name it something like pad() and pass it an int with the string like this:

public static String pad(String name, int length){
   StringBuilder fullName = new StringBuilder(name);
   while (fullName.length()!=length){
      fullName.append(" ");
   }
   return fullName.toString();
}

And use this one method for all the lines

Anthony Chalk

Level 30 , London, United Kingdom

20 January 2020, 16:13

I changed lines 19-46 to:

ArrayList<String> fileData = allProducts(fileName);

    if (args[0].equals("-c")){
        String productID = getID(fileData);
        String productName = fullName(args[1]);
        String productPrice = fullPrice(args[2]);
        String productQuantity = fullQuantity(args[3]);
        String product = productID + productName + productPrice + productQuantity;

        fileData.add(product);

        for (String s : fileData){
            writer.write(s);
            writer.newLine();
        }
    }

    reader.close();
    fileOutputStream.close();
    writer.close();
}
//get ID
public static String getID(ArrayList<String> products) throws Exception {
    ArrayList<Integer> productIDs = productIDs(products);
    int id = productIDs.get(productIDs.size()-1) +1;
    return fullID(id);
}

and it's still failing. I did sort the IDs, on line 54

Guadalupe Gagnon

Level 37 , Tampa, United States

20 January 2020, 16:21

useful

Try this:

public static void main(String[] args) throws Exception {
       if (!args[0].equals("-c")) return;
       BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
       String fileName = reader.readLine();
       reader.close();
       ArrayList<String> fileData = allProducts(fileName);
       FileOutputStream fileOutputStream = new FileOutputStream(fileName);
       BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(fileOutputStream));

       String productID = getID(fileData);
       String productName = fullName(args[1]);
       String productPrice = fullPrice(args[2]);
       String productQuantity = fullQuantity(args[3]);
       String product = productID + productName + productPrice + productQuantity;

       fileData.add(product);

       for (int i = 0; i < fileData.size()-1; i++) {
           writer.write(fileData.get(i));
           writer.newLine();
       }
       writer.write(fileData.get(fileData.size()-1));

       fileOutputStream.close();
       writer.close();
   }

Two main changes: 1) moved the check for "-c" to the beginning of the code in case it isn't there. No need to run the program if this is missing 2) when opening a new stream for writing to a file, it will erase all the data contained in that file. This means if you open the 'write' stream before reading the data from it there will be no data there for the 'read' stream.

Anthony Chalk

Level 30 , London, United Kingdom

20 January 2020, 16:45

Thank you, I didn't realise that with regards to point 2. Unfortunately, it's still not validating

Guadalupe Gagnon

Level 37 , Tampa, United States

20 January 2020, 16:51

One last thing I just noticed. Closing the streams are interfering with eachother. Try this, cross your fingers, and hope the stars align:

BufferedWriter writer = new BufferedWriter(new FileWriter(fileName));
for (int i = 0; i < fileData.size()-1; i++) {
   writer.write(fileData.get(i));
   writer.newLine();
}
writer.write(fileData.get(fileData.size()-1));

writer.close();

Anthony Chalk

Level 30 , London, United Kingdom

20 January 2020, 17:03

Thanks, but I'm afraid not Edit: I also tried your trick of refreshing the task then copy-pasting the solution - no luck there either

Guadalupe Gagnon

Level 37 , Tampa, United States

20 January 2020, 17:17

are the same 3 items failing?

Guadalupe Gagnon

Level 37 , Tampa, United States

20 January 2020, 17:17

and could you copy/paste your current code?

Guadalupe Gagnon

Level 37 , Tampa, United States

20 January 2020, 20:39

useful

I found one more bug. There was a lot of back and forth in this thread, so I'll list everything using the original code you shared: #1 line 70 using '!=' and not .equals() to check for null value #2 not using append on line 16. #2a modifying code so that all the contained data in the file is read in and saved, then re-written to file after the read. #3 Closing the 2 streams on line 37 and 38. You should be able to just reverse those 2 lines and have everything legit #4 **NEW** line 60 grabs the first 7 digits of the line where the ID's are 8 digits long. I noticed that the line with the new product had id "1984799" instead of "19847984" because of this (using the data from the example).

Anthony Chalk

Level 30 , London, United Kingdom

20 January 2020, 20:59

Thank you. Here's my new code:

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 {
        if (!args[0].equals("-c")) return;
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String fileName = reader.readLine();
        reader.close();
        ArrayList<String> fileData = allProducts(fileName);


        String productID = getID(fileData);
        String productName = fullName(args[1]);
        String productPrice = fullPrice(args[2]);
        String productQuantity = fullQuantity(args[3]);
        String product = productID + productName + productPrice + productQuantity;

        fileData.add(product);

        BufferedWriter writer = new BufferedWriter(new FileWriter(fileName));
        for (int i = 0; i < fileData.size() - 1; i++) {
            writer.write(fileData.get(i));
            writer.newLine();
        }
        writer.write(fileData.get(fileData.size() - 1));

        writer.close();
    }

Anthony Chalk

Level 30 , London, United Kingdom

20 January 2020, 21:00

//get ID
    public static String getID(ArrayList<String> products) {
        ArrayList<Integer> productIDs = productIDs(products);
        int id = productIDs.get(productIDs.size()-1) +1;
        return fullID(id);
    }

    //return sorted ArrayList of product IDs
    public static ArrayList<Integer> productIDs(ArrayList<String> list) {
        ArrayList<Integer> productIDs = new ArrayList<>();
        for (String string : list){
            productIDs.add(getProductID(string));
        }
        Collections.sort(productIDs);
        return productIDs;
    }

    //get the ID of a product
    public static int getProductID(String product){
        String productIDString = product.substring(0, 8);
        return Integer.parseInt(productIDString.replaceAll(" ", ""));
    }

    // return ArrayList of all products in the file
    public static ArrayList<String> allProducts(String fileName) throws Exception{
        BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(fileName)));
        ArrayList<String> products = new ArrayList<>();
        String s;
        while ((s = reader.readLine()) != null ){
            products.add(s);
        }
        reader.close();
        return products;
    }
}

now only the 3rd condition is failing

Guadalupe Gagnon

Level 37 , Tampa, United States

20 January 2020, 21:16

Maybe:

if (!args[0].equals("-c") || args.length != 4) return;

If that doesn't work, try putting this line of code directly after reading from the file (line 18 of the post 2 posts above)

Anthony Chalk

Level 30 , London, United Kingdom

20 January 2020, 21:24

Alas it's still failing condition 3

Guadalupe Gagnon

Level 37 , Tampa, United States

20 January 2020, 21:30

solution

I'm literally banging my head against the keyboard. I can imagine how you feel....

Anthony Chalk

Level 30 , London, United Kingdom

20 January 2020, 21:34

I surrounded line 18 (5 posts above) to the end of the main method with

if(args.length>0)

and it passed thank you so much for all your help