Thread: caesar box with length of non-square...

public static String encrypt(String plainText) {
int a = plainText.length();
// Determining the size of the Array
// Rounding up square root of text length
int SizeOfArray = ((int) Math.ceil(Math.sqrt(a)));

// Setting the size of the Array
char[][] encryptArray = new char[SizeOfArray][SizeOfArray];

for (int i = 0; i < SizeOfArray; i++) {
for (int j = 0; j < SizeOfArray; j++) {
encryptArray[i][j] = plainText.charAt(0);
plainText = plainText.substring(1);
}
}

String putTogether = "";

for (int i = 0; i < SizeOfArray; i++) {
for (int j = 0; j < SizeOfArray; j++) {
putTogether += encryptArray[j][i];
}
}
return putTogether;
}

The code works perfectly with perfect square length

but it gives error with non square length..
Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 0
at java.lang.String.charAt(String.java:686)

Please Help!