Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 26

Question

I am getting the error Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 26 in my code when i try to run certain letters (e) and i dont know how to resolve it.

The array contains 26 characters(each letter of the alphabet). Can anybody see the problem in the code?

//Breaking up the letters from the input and placing them in an array
char[] plaintext = input.toCharArray();
//For loops that will match length of input against alphabet and move the letter 14 spaces
for(int i = 0;i<plaintext.length;i++) {
    for(int j = 0 ; j<25;j++) {
        if(j<=12 && plaintext[i]==alphabet[j]) {
            plaintext[i] = alphabet[j+14];
            break;
        }
        //Else if the input letter is near the end of the alphabet then reset back to the start of the alphabet
        else if(plaintext[i] == alphabet[j]) {
            plaintext[i] = alphabet [j-26];
        }
    }
}

Arrays start at 0. If it contains 26 entrys it will be in range 0-25 — John Snow
– John Snow, Commented May 6, 2013 at 12:32

Magnilex · Accepted Answer · 2013-05-06 12:46:23Z

4

if(j<=12 && plaintext[i]==alphabet[j]) {
     plaintext[i] = alphabet[j+14];
     break;
}

This code will access alphabet[26] if j == 12 and plaintext[i]==alphabet[j]. Your array has indexes 0-25. Java arrays have zero based indexes.

edited May 6, 2013 at 12:46

answered May 6, 2013 at 12:33

Magnilex

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4 Comments

d99 Over a year ago

Thanks, the encryption is now working but now the decryption is giving the wrong output after the 14th letter. What do I need to change? ive updated the code for decrytion above.

Magnilex Over a year ago

@d99 This is a totally different question. Please accept any answer here, they are all more or less equally helpful. Then try to solve it yourself. After that, ask another question if needed.

d99 Over a year ago

Sorry, I tried it myself but cant really find what's wrong and I thought it would be relevant. I've accepted your answer, thanks.

Magnilex Over a year ago

No worries, but I recommend you to carefully think through your solution and possibly try a different approach. You will learn a lot more that way, and end up a better coder. :)

Michal Borek · Accepted Answer · 2013-05-06 12:32:22Z

3

If it contains 26 characters (as you said) then the last index is 25 not 26. That causes the problem.

You have j<=12 so when j is 12 then you have index 26 (j+14) and that is out of array.

answered May 6, 2013 at 12:32

Michal Borek

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Comments

Marko Topolnik · Accepted Answer · 2013-05-06 12:33:41Z

3

You have the edge case where j == 12 and you dereference alphabet[j+14] == alphabet[26].

answered May 6, 2013 at 12:33

Marko Topolnik

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Comments

Maroun · Accepted Answer · 2013-05-06 12:33:50Z

3

When j is 12, you'll get 26. Since arrays in Java are zero-based arrays, your array indexes are from 0 to 25, so 26 is outOfBounds.

  if(j<=12 && plaintext[i]==alphabet[j]){
     //Check if j+14 doesn't exceed 25

Another thing, your for loops should be for(int j = 0 ; j<26;j++){ (don't worry, 25 is the last index).

BTW, the exception you're getting is very informative. Using a debugger will help a lot in cases like this.

answered May 6, 2013 at 12:33

Maroun

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