loops with arrayList bug java

Question

I am not sure why I am getting this problem. But basically I am shuffling a word and I am using an arrayList with loops.

This is my code and for debugging purposes I added a couple of lines.

//Declare and Initialize an arrayList for character checking
      ArrayList<Boolean> jumbleVerfiy = new ArrayList<Boolean>();
      for(int x = 0; x < chosenWord.length(); x++)
          jumbleVerfiy.add(false);

      while((chosenWord.length()) != (jumbledWord.length()))
      {
          //Generate random number for getting the random character
          int verficationNumber = rnd.nextInt(chosenWord.length());

          //Checks if the random number generated has been used before
          if(jumbleVerfiy.get(verficationNumber) == false)
          {
              //Get the character from the randomly generated number and change the boolean array to keep track of
              //letters used
              jumbledWord += chosenWord.charAt(verficationNumber);
              System.out.print(jumbleVerfiy.get(verficationNumber) + " " + verficationNumber);//debug
              jumbleVerfiy.add(verficationNumber, true);
              System.out.println(" " + jumbledWord + " " + jumbleVerfiy.get(verficationNumber));//debug
          }

My output is as follows

false 3 r true
false 4 ry true
false 2 ryr true
false 1 ryra true
false 4 ryray true
tarry ryray

In this output 4 was changed to true on the second run but then when it loops it is set to false for some reason. So I keep getting a duplicate letter. I am not sure what the problem is. Would love some insight.

Thank you,

Joni · Accepted Answer · 2013-10-04 06:02:28Z

2

You are adding values to the list, not setting them:

jumbleVerfiy.add(verficationNumber, true);

This means that if you for example first choose the second letter and then the second, the list ends up looking like (T,F,T,..) as if you had chosen the first and the third.

You need to use:

jumbleVerfiy.set(verficationNumber, true);

answered Oct 4, 2013 at 6:02

Joni

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Comments

Brandon Buck · Accepted Answer · 2013-10-04 06:04:37Z

1

In your loop you are mistakenly adding a new value to the array when you should be setting a value. The offending line:

jumbleVerfiy.add(verficationNumber, true);

Which should be calling set(index, value) instead. This should resolve your problem. You also might think of using a array instead of an ArrayList to avoid the overhead associated with the ArrayList since you don't need to expand once it's been initialized.

That would be:

boolean[] jumbleVerify = new boolean[chosenWord.length()];

answered Oct 4, 2013 at 6:04

Brandon Buck

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Comments

Scary Wombat · Accepted Answer · 2013-10-04 06:02:20Z

0

In your code you need to use

jumbleVerfiy.set(verficationNumber, true);

other it will just get added to the arrayList

answered Oct 4, 2013 at 6:02

Scary Wombat

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1 Comment

Jon Skeet Over a year ago

No, it won't get added to the end - it will be inserted at the specified location.

nurisezgin · Accepted Answer · 2013-10-04 06:03:52Z

0

Because you setted new item to arraylist with index( add(index, value) ). If you set item ex. index 3, then index 3 old item went to be index 4.

answered Oct 4, 2013 at 6:03

nurisezgin

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Jan Pešta · Accepted Answer · 2013-10-04 06:05:19Z

0

I think your problem is that you are using:

jumbleVerfiy.add(verficationNumber, true);

which adds value on position. Use following instead and should work:

jumbleVerfiy.set(verficationNumber, true);

answered Oct 4, 2013 at 6:05

Jan Pešta

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