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java.lang.ArrayIndexOutOfBoundsException when I make a string of characters

Ok so I'm trying to generate a random character generator that goes beyond simple numbers and letters. I want to simultaneously create a replica of that same generator for the purpose of comparing them and having it print out how many attempts it took for "Cracker" to match the value of "Generator" because I'm interested in the concept after reading a bit of cryptography. When parsing the characters to a string, I get an OutOfBoundsException, but why? I can't seem to find much on the limitations of string. I would think it would have to been an issue besides the string not being able to take the characters but I can't figure it out.
import java.util.Random;
public class Class {
public static void Generator(){
Random r = new Random();
String[] cArray = new String[10];
for(int i = 0; i <= cArray.length; i++){
char c = (char)(r.nextInt(200) + 'a');
String y = Character.toString(c);
cArray[i] = y;
System.out.print(cArray[i]);
}
}
public static void Cracker(){
Random s = new Random();
String[] bArray = new String[10];
for(int x = 0; x <= bArray.length; x++){
char b = (char)(s.nextInt(100) + 'a');
String z = Character.toString(b);
bArray[x] = z;
System.out.print(bArray[x]);
}
}
public static void main(String[] args) {
Generator();
}
}
Any help would be appreciated.

for (int i = 0; i <= cArray.length; i++)
^^^^
Change to
for (int i = 0; i < cArray.length; i++)
^^^^
In both your for loops.
An array of length n has elements from 0 to n-1 - i.e. array arr of length 3 has elements arr[0], arr[1] & arr[2].

Array out of bound in Java

I am trying to count the number of each character from a to z in a random array of chars of size 100.
import java.util.Random;
public class RandomChars {
public static void main(String[] args) {
Random r = new Random();
String chars= "abcdefghijklmnopqrtuvwxyz";
String[] countc = new String[26];
char[] charArray = new char[100];
for(int i = 1;i<=100;i++)
{
charArray[i-1]=chars.charAt(r.nextInt(chars.length()));
System.out.print(chars.charAt(r.nextInt(chars.length())));
if(i%20==0)
{
System.out.println("");
}
}
//System.out.println(charArray.length);
int m = 0;
int p=0;
for(int n = 0;n<100;n++)
{
char xx = chars.charAt(n);
m = 0;
p=0;
do
{
if(charArray[m]==xx)
{
p=p+1;
}
m=m+1;
}while(m<=charArray.length);
countc[n]=""+p+""+xx;
}
System.out.println("The count of each character is "+ countc);
}
}

> for(int n = 0;n<100;n++)
should be
for (int n =0; n<99; n++)
charArray = 0 to 99 (i-1), but subroutine below you are going 0 to 100 (int n)

do
{
/* ... */
}while(m<=charArray.length);
On the last iteration, m will be equal to charArray.length, so when you call charArray[m], it'll be out of bounds. Change it to while(m < charArray.length); instead.

Change this:
m<=charArray.length
To this:
m<charArray.length

char xx = chars.charAt(n); is getting called all the way up to 99 when chars.charAt() can take a max argument of 25. You need to fix your loop logic so that you check all 100 elements for each of the 26 possible characters, not the other way around.
EDIT: Same thing is happening on your do..while loop.

Firstly, your String chars is omitting the 's' so I've added it in and updated the code to work slightly differently.
After creating the charArray it iterates over each character 26 times (once for each letter). There's probably a much better way to do this but I'm not so hot on Java.
import java.util.Random;
import java.util.Arrays;
public class RandomChars {
public static void main(String[] args) {
Random r = new Random();
String chars= "abcdefghijklmnopqrstuvwxyz";//added the 's'?
String[] countc = new String[26];
char[] charArray = new char[100];
for(int i=0; i<100; i++){
charArray[i]=chars.charAt(r.nextInt(chars.length()));
System.out.print(charArray[i]);
if((i+1)%20==0){
System.out.println("");
}
}
for(int n=0; n<26; n++){//for each of the 26 chars
char xx = (char)chars.charAt(n);
int p=0;
for(int a=0; a<100; a++){//loop through the charArray and count the matches
if(charArray[a]==xx){
p++;
}
}
countc[n]=""+xx+":"+p;
}
System.out.println("The count of each character is "+Arrays.toString(countc));
}
}
http://runnable.com/VCRLPa-2kdoqq2dW/stackoverflow-com-questions-26042877-for-java

Non-repeating random numbers inside array JAVA

I would like to generate 6 numbers inside an array and at the same time, having it compared so it will not be the same or no repeating numbers. For example, I want to generate 1-2-3-4-5-6 in any order, and most importantly without repeating. So what I thought is to compare current array in generated array one by one and if the number repeats, it will re-run the method and randomize a number again so it will avoid repeating of numbers.
Here is my code:
import javax.swing.*;
public class NonRepeat
{
public static void main(String args[])
{
int Array[] = new int [6];
int login = Integer.parseInt(JOptionPane.showInputDialog("ASD"));
while(login != 0)
{
String output="";
for(int index = 0; index<6; index++)
{
Array[index] = numGen();
for(int loop = 0; loop <6 ; loop++)
{
if(Array[index] == Array[loop])
{
Array[index] = numGen();
}
}
}
for(int index = 0; index<6; index++)
{
output += Array[index] + " ";
}
JOptionPane.showMessageDialog(null, output);
}
}
public static int numGen()
{
int random = (int)(1+Math.random()*6);
return random;
}
}
I've been thinking it for 2 hours and still cant generate 6 numbers without repeating.
Hope my question will be answered.
Btw, Im new in codes so please I just want to compare it using for loop or while loop and if else.

You can generate numbers from, say, 1 to 6 (see below for another solution) then do a Collections.shuffle to shuffle your numbers.
final List<Integer> l = new ArrayList<Integer>();
for (int j = 1; j < 7; j++ ) {
l.add( j );
}
Collections.shuffle( l );
By doing this you'll end up with a randomized list of numbers from 1 to 6 without having twice the same number.
If we decompose the solution, first you have this, which really just create a list of six numbers:
final List<Integer> l = new ArrayList<Integer>();
for (int j = 1; j < 7; j++ ) {
l.add( j );
}
So at this point you have the list 1-2-3-4-5-6 you mentioned in your question. You're guaranteed that these numbers are non-repeating.
Then you simply shuffle / randomize that list by swapping each element at least once with another element. This is what the Collections.shuffle method does.
The solutions that you suggested isn't going to be very efficient: depending on how big your list of numbers is and on your range, you may have a very high probability of having duplicate numbers. In that case constantly re-trying to generate a new list will be slow. Moreover any other solution suggesting to check if the list already contains a number to prevent duplicate or to use a set is going to be slow if you have a long list of consecutive number (say a list of 100 000 numbers from 1 to 100 000): you'd constantly be trying to randomly generate numbers which haven't been generated yet and you'd have more and more collisions as your list of numbers grows.
If you do not want to use Collections.shuffle (for example for learning purpose), you may still want to use the same idea: first create your list of numbers by making sure there aren't any duplicates and then do a for loop which randomly swap two elements of your list. You may want to look at the source code of the Collections.shuffle method which does shuffle in a correct manner.
EDIT It's not very clear what the properties of your "random numbers" have to be. If you don't want them incremental from 1 to 6, you could do something like this:
final Random r = new Random();
final List<Integer> l = new ArrayList<Integer>();
for (int j = 0; j < 6; j++ ) {
final int prev = j == 0 ? 0 : l.get(l.size() - 1);
l.add( prev + 1 + r.nextInt(42) );
}
Collections.shuffle( l );
Note that by changing r.nextInt(42) to r.nextInt(1) you'll effectively get non-repeating numbers from 1 to 6.

You have to check if the number already exist, you could easily do that by putting your numbers in a List, so you have access to the method contains. If you insist on using an array then you could make a loop which checks if the number is already in the array.
Using ArrayList:
ArrayList numbers = new ArrayList();
while(numbers.size() < 6) {
int random = numGen(); //this is your method to return a random int
if(!numbers.contains(random))
numbers.add(random);
}
Using array:
int[] numbers = new int[6];
for (int i = 0; i < numbers.length; i++) {
int random = 0;
/*
* This line executes an empty while until numGen returns a number
* that is not in the array numbers yet, and assigns it to random
*/
while (contains(numbers, random = numGen()))
;
numbers[i] = random;
}
And add this method somewhere as its used in the snippet above
private static boolean contains(int[] numbers, int num) {
for (int i = 0; i < numbers.length; i++) {
if (numbers[i] == num) {
return true;
}
}
return false;
}

Here is the solution according to your code -
You just need to change the numGen method -
public static int numGen(int Array[])
{
int random = (int)(1+Math.random()*6);
for(int loop = 0; loop <Array.length ; loop++)
{
if(Array[loop] == random)
{
return numGen(Array);
}
}
return random;
}
Complete code is -
import javax.swing.*;
public class NonRepeat
{
public static void main(String args[])
{
int login = Integer.parseInt(JOptionPane.showInputDialog("ASD"));
while(login != 0)
{
int Array[] = new int [6];
String output="";
for(int index = 0; index<6; index++)
{
Array[index] = numGen(Array);
}
for(int index = 0; index<6; index++)
{
output += Array[index] + " ";
}
JOptionPane.showMessageDialog(null, output);
}
}
public static int numGen(int Array[])
{
int random = (int)(1+Math.random()*6);
for(int loop = 0; loop <Array.length ; loop++)
{
if(Array[loop] == random)
{
return numGen(Array);
}
}
return random;
}
}

Use List instead of array and List#contains to check if number is repeated.

you can use a boolean in a while loop to identify duplicates and regenerate
int[] array = new int[10]; // array of length 10
Random rand = new Random();
for (int i = 0 ; i < array.length ; i ++ ) {
array[i] = rand.nextInt(20)+1; // random 1-20
boolean found = true;
while (found) {
found = false;
// if we do not find true throughout the loop it will break (no duplicates)
int check = array[i]; // check for duplicate
for (int j = 0 ; j < i ; j ++) {
if ( array[j] == check ) {
found = true; // found duplicate
}
}
if (found) {
array[i] = rand.nextInt(20)+1 ; // replace
}
}
}
System.out.println(Arrays.toString(array));

You may use java.util.Random. And please specify if you want any random number or just the number 1,2,3,4,5,6. If you wish random numbers then , this is a basic code:
import java.util.*;
public class randomnumber
{
public static void main(String[] args)
{
Random abc = new Random();
int[] a = new int[6];
int limit = 100,c=0;
int chk = 0;
boolean y = true;
for(;c < 6;)
{
int x = abc.nextInt(limit+1);
for(int i = 0;i<a.length;i++)
{
if(x==a[i])
{
y=false;
break;
}
}
if(y)
{
if(c!=0)if(x == (a[c-1]+1))continue;
a[c]=x;
c++;
}
}
for (Integer number : a)
{
System.out.println(number);
}
}
}
if you don't understand the last for loop , please tell , i will update it.

Use List and .contains(Object obj) method.
So you can verify if list has the random number add before.
update - based on time you can lost stuck in random loop.
List<Integer> list = new ArrayList<Integer>();
int x = 1;
while(x < 7){
list.add(x);
x++;
}
Collections.shuffle(list);
for (Integer number : list) {
System.out.println(number);
}
http://docs.oracle.com/javase/7/docs/api/java/util/List.html#contains(java.lang.Object)

How do I take null spaces out of an array?

I have to make a program that takes duplicate characters from an input array and prints out a new array with all unique characters.
It all works. Except when characters are taken out, it leaves an empty box at the end of that new array.
public class Deleter {
public static void main (String[] args){
Scanner keyboard = new Scanner(System.in);
char[] initialInputArray = new char[15];
System.out.println("How many characters do you wish to enter?");
int size = keyboard.nextInt();
while ( size > initialInputArray.length ) {
System.out.println("Error. Enter smaller number.");
size = keyboard.nextInt();
}
if( initialInputArray.length <= 15) {
for ( int counter = 0; counter < size; counter++ ){
initialInputArray[counter] = keyboard.next().charAt(0);
}
{
}
}
deleteRepeats(initialInputArray, size);
//Comeback to print out array
{
for ( int helloWorld = 0 ; helloWorld < size ; helloWorld ++)
System.out.print( initialInputArray[helloWorld] );
}
}
//"deleteReapets" method begins, looking for repeated user inputs
public static char[] deleteRepeats (char[] methodArray, int sizeTwo) {
if (sizeTwo == 0)
return methodArray;
if (sizeTwo == 1)
return methodArray;
int uniqueCharacter = 1;
//Start at the second entered character.
for (int x = 1; x < sizeTwo; ++x) {
int y;
for (y = 0; y < uniqueCharacter; ++y) {
if (methodArray[x] == methodArray[y]) break; // break if we find duplicate.
}
if (y == uniqueCharacter) {
methodArray[uniqueCharacter] = methodArray[x]; // add
++uniqueCharacter; // increment uniqueCharacter...[0,uniqueCharacter) is still "unique char list"
}
}
while ( uniqueCharacter < sizeTwo ) {
methodArray[uniqueCharacter] = 0;
uniqueCharacter++;
}
return methodArray;
}
}

That empty box is the null characters that you added at the end of the array. You are printing them because you are not adjusting size according to the number of unique characters (which can be less than the input size). Since you aren't creating a new array, you don't need to return a char [] from deleteRepeats. Instead, you can return the number of unique characters. That way, the calling program knows how many to print.
If your assignment requires that deleteRepeats return a char[], then you should allocate a new array that has a length exactly equal to uniqueCharacter, copy the unique characters to it, and return that. The calling program can just print that new (and shorter) array, rather than printing the first size elements of the input.

Probably the easiest way would be to make a new array to the size of your array of chars and then copy all of the chars into that. The problem with arrays is that once they have been initialized they can't be re sized. If your are familiar with arrayLists I would recommend using them. But if not try something like this...
int count = 0;
for(int i = 0; i < initialInputArray.size; i++){
count++;
}
char[] newArray = new char[count];
for(int i = 0; i < count; i++){
newArray[i] = initialInputArray[i];
}

I would suggest using a HashSet to remove duplicates and wrapping your char to Character. Something like this:
public static Character[] deleteRepeats (char[] methodArray){
HashSet<Character> set = new HashSet<Character>();
for(int index = 0; index < methodArray.length; index++){
set.add(methodArray[index]);
}
return set.toArray(new Character[set.size()]);
}
So in your main method, what you would do is something like this:
Character[] charArray = deleteRepeats(methodArray);
for(int index = 0; index < charArray.length; index++){
System.out.println(charArray[index]);
}

Printing letters in 2D arrays? First letter not showing

I'm hoping someone can answer this so I'll try to explain this well.
My goal is to generate a MAXIMUM of 3 unique vowels (AEIOU) on a line of 5 squares. I have made 25 squares using a 2D array (board[][]), but I want to do the first line first. Picture it like this:
Now, my problem is, whenever I try to generate random letters in my squares, the first letter doesn't show. For example I have E and O, O would only show in my squares, and not E. It's printing in my console, but not in my GUI.
Also, sometimes DUPLICATES of letters are showing. I don't know how to fix this :|
Here are the codes I've done so far:
String board[][] = new String[5][5];
String alphabet = "AEIOU";
int numArray[] = new int[5]; //where I can store random indices of alphabet
int finalIndex = 0;
int random = (int) (Math.random()*3) + 1; //random number of vowels to be generated
//this loop covers everything
for(int ctr = 0; ctr < random; ctr++) {
while(ctr != finalIndex) { //checks if there are any duplicates
int rand = (int) (Math.random()*4); //random position for the letter
numArray[ctr] = rand;
while(numArray[ctr] != numArray[finalIndex]) {
finalIndex++;
}
}
//finds the position of the letter in alphabet and converts it to String
char character = alphabet.charAt(numArray[ctr]);
String s = String.valueOf(character);
System.out.println(s);
//loop for putting the letters to the 2D array
for(int i = 0; i < board.length; i++) {
int gen = (int) (Math.random()*4); //random square for letter
for(int j = 0; j <= gen; j++) {
if(i == 0 && j < 5) { //row 1
board[i][gen] = s;
}
}
}
}
I decided not to put my GUI code anymore just to make things simpler.

Sorry I couldn't read what you had, so i tried this myself...
int rows = 5;
Character [] vowels = {'A','E','I','O','U'};
Character [][] board = new Character [vowels.length][rows];
for(int row = 0;row<rows;row++){
ArrayList<Character> tempVowels = new ArrayList<Character>(Arrays.asList(vowels));
int numVowPerLine = (int)Math.floor(Math.random()*4);
for(int j = 0;j<numVowPerLine;j++){
do{
int pos = (int)Math.floor(Math.random()*5);
if(board[row][pos] == null){
int temp = (int)Math.floor(Math.random()*tempVowels.size());
board[row][pos] = tempVowels.get(temp);
tempVowels.remove(temp);
break;
}
}while(true);
}
}