Level 41

21.06.2021
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17comments

Running the program keeps throwing this error. Anyone know why?

Question about the task

Under discussion

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space at java.base/java.util.Arrays.copyOf(Arrays.java:3536) at java.base/java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:227) at java.base/java.lang.AbstractStringBuilder.appendNull(AbstractStringBuilder.java:637) at java.base/java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:590) at java.base/java.lang.StringBuilder.append(StringBuilder.java:173) at com.codegym.task.task32.task3213.Solution.decode(Solution.java:36) at com.codegym.task.task32.task3213.Solution.main(Solution.java:18) Process finished with exit code 1

Hi, Amigo. You know we're being followed. They're looking through our mail. So we need to encrypt our traffic.
Implementing a Caesar cipher won't be hard for you. Let me remind you that this is simply a right-shift along the alphabet by the number of letters indicated by the key parameter.
The main() method has a good example.

Implement the String decode(StringReader reader, int key) method.
The method receives encoded data.
It must return the decrypted string stored in the StringReader.
Under no circumstances should null be returned.
The main() method is not tested.

Requirements:

The Solution class must have a String decode(StringReader reader, int key) method.
The decode(StringReader reader, int key) method must return the decrypted string stored in the StringReader.
Under no circumstances should null be returned.

package com.codegym.task.task32.task3213; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.io.StringReader; import java.util.Arrays; import java.util.Collections; /* Caesar cipher */ public class Solution { public static void main(String[] args) throws IOException { StringReader reader = new StringReader("Khoor#Dpljr#&C,₷B'3"); System.out.println(decode(reader, -3)); // Hello Amigo #@)₴?$0 } public static String decode(StringReader reader, int key) throws IOException { /** * return the decrypted string stored inside the reader * take the string from the string reader * transform it into a character array * take each character and shift it according to int key * transform the character array back into a string * return that string * if not possible return a string anyway */ String result = new String(); if (reader != null) { BufferedReader bufferedReader = new BufferedReader(reader); StringBuilder sb = new StringBuilder(); while (bufferedReader.ready()){ sb.append(bufferedReader.readLine()); } char[] charsOfString = sb.toString().toCharArray(); for (int i = 0; i < charsOfString.length; i++) { int charValue = charsOfString[i] + key; charsOfString[i] = (char) charValue; } result = Arrays.toString(charsOfString); } return result; } }

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Thomas

Level 41 , Bayreuth, Germany

21 June 2021, 10:05

StringReader ready works differnt than you expect. It just tells you if the next read won't block. For a StringReader that is always true. So you should do a different check like:

String s = null;
while((s = bufferedReader.readLine()) != null ) {

As with your other task readLine surpresses linebreaks. As it is hard to guess if there are some missing (if it is a one liner) I think it is better here to read char by char. Then you won't need an array but could add the key while reading and therefore saving the result directly into your StringBuilder Again this is just guessing ;)

Andrei

Level 41

21 June 2021, 11:23

But I am using the ready method on a buffered reader. Doesn't that matter?

Andrei

Level 41

21 June 2021, 11:25

I changed the loop to this but still no validation;

String line;
            while ((line = bufferedReader.readLine()) != null){
                sb.append(line);
            }

Thomas

Level 41 , Bayreuth, Germany

21 June 2021, 11:26

useful

the BufferedReaders ready method uses the one of the underlaying stream

Andrei

Level 41

21 June 2021, 11:27

I see, ok, so it goes down the line until the last available reader.

Thomas

Level 41 , Bayreuth, Germany

21 June 2021, 11:55

if it still not validates then I'd read from the stream char by char as mentioned above. That way you do not have the linebreak problem (and the resulting code is much shorter)

Andrei

Level 41

21 June 2021, 11:58

What do you think of this? Still doesn't validate.

if (reader != null) {
           BufferedReader bufferedReader = new BufferedReader(reader);
           StringBuilder sb = new StringBuilder();
           char[] otherChar = new char[1];
           int count = 0;
           while (!(bufferedReader.read(otherChar) == -1)) {
                   ++count;
                   sb.append(String.valueOf(otherChar[0] + key));
           }

           result = sb.toString();
       }
       return result;

Thomas

Level 41 , Bayreuth, Germany

21 June 2021, 12:07

line 6, here you assign the read value to a reference. You probably wanted to write otherChar[0] (that should make it validate). Better however would be to change otherChar to a primitive char and to remove count (as it is not needed anymore).

Andrei

Level 41

21 June 2021, 12:12

I tried writing otherChar[0] but it won't be accepted. I also tried to read to a simple char but i couldn't find a method in bufferedreader that reads strictly a char. I thought that by passing otherChar it reads straight into the array.

Andrei

Level 41

21 June 2021, 12:15

Wait, I am on to something, I have found out how to read a single char but I am trying to find out how I compare it to -1

Andrei

Level 41

21 June 2021, 12:16

char otherChar;
while (!((otherChar = bufferedReader.read()) == -1)) {

This isn't accepted although it's not clear to me why because read() reads a single char and a char can be compared to int.

Thomas

Level 41 , Bayreuth, Germany

21 June 2021, 12:17

make the char an int... and then sb.append((char) (otherChar + key));

Andrei

Level 41

21 June 2021, 12:21

Still not accepted

while (!(bufferedReader.read() == -1)) {
                   char newChar = (char) (bufferedReader.read() + key);
                   sb.append(newChar);
           }

Andrei

Level 41

21 June 2021, 12:32

I didn't even need a buffered reader....

StringBuilder sb = new StringBuilder();
     int ch1;
     if (reader != null) {
         while ((ch1 = reader.read()) != -1) {
             char newChar = (char) (ch1);
             sb.append((char) (newChar + key));
         }
     }
     return sb.toString();

Andrei

Level 41

21 June 2021, 12:32

Thanks for the help!

Guadalupe Gagnon

Level 37 , Tampa, United States

21 June 2021, 13:41

useful

Just a little tip: Put the method comments outside the method. With the comment that you used it allows intelliJ's popup to include that information. See pic:

Andrei

Level 41

21 June 2021, 15:17

You mean a PRO tip? Nice, thanks! 👍😁