During doing h,w with Java, an error about String range has raised

I made the codes for a credit card tester. while I compile these codes, it has been compiled successfully. however, when I enter 12 digits of credit card numbers, it showed a message: Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 11. I would really appreciate it if you guys tell me what has been wrong on the codes. Thank you

  public class CreditCard{
private String cardNumber; //The credit card number is stored as String.
private boolean valid; //To indicate valid or not
int errorCode; //instance variable 
// initializing instance variables
public CreditCard(String creditCardNumber){
cardNumber = creditCardNumber;  
valid = true; //initial instance = true, assumes that inputted numbers can be false 
errorCode = 0;
} 
public void check1(){
//The first digit must be a 4.
if(cardNumber.charAt(0) != 4){
valid = false;
errorCode = 1; //case 1 error 
return;
}
}
public void check2(){
//The fourth digit must be one greater than the fifth digit  int fourth = Integer.parseInt(4,5)
int fourth = Integer.parseInt(cardNumber.substring(4,5));
int fifth = Integer.parseInt(cardNumber.substring(5,6));
if(fourth != fifth + 1){
valid = false;
errorCode = 2;
return;
}
}
public void check3(){
//The product of the first, fifth, and ninth digits must be 24
int first = Integer.parseInt(cardNumber.substring(1,2));
int fifth = Integer.parseInt(cardNumber.substring(5,6));
int ninth = Integer.parseInt(cardNumber.substring(9,10));
if(first * fifth * ninth != 24){
valid = false;
errorCode = 3;
return;
}
}
public void check4(){
//The sum of all digits must be evenly divisible by 4
int sum = 0; //initiate variable sum
for(int i=0; i<cardNumber.length(); i++  )
sum = sum + Character.getNumericValue(cardNumber.charAt(i));
if(sum % 4 != 0){
valid = false;
errorCode = 4;
return;
}
}
public void check5(){
// The sum of the first four digits must be one less than the sum of the last four digits
int sumFirst = 0;
int sumLast = 0;
for(int i = 0; i<4; i++)
sumFirst = sumFirst + Character.getNumericValue(cardNumber.charAt(i));
for(int i = 0, j = cardNumber.length(); i<4; i++, j-- )
sumLast = sumLast + Character.getNumericValue(cardNumber.charAt(j));
if(sumFirst != sumLast - 1){
valid = false;
errorCode = 5;
return;
}
}
public void check6(){
//If you treat the first two digits as a two-digit number, and the seventh and eight digits as a two digit number, their sum must be 100. 
int first = Integer.parseInt(cardNumber.substring(0,2));
int seight = Integer.parseInt(cardNumber.substring(8,10));
if(first + seight != 100){
valid = false;
errorCode = 6;
return;
}
}
public void check(){
check1();
check2();
check3();
check4();
check5();
check6();
}
public boolean isValid(){
return valid;
}    
public int getErrorCode(){
return errorCode; 
}
}

when u get length of string its array of chars start from zero and end in length-1;

in your fifth check you accessed the char at index j that basically is outside of range of string array

Hi besides the Index Out of Bound Error, I think you missed something in the check1() method.

If the cardNumber is stored as string, the line if(cardNumber.charAt(0) != 4){ should be if(cardNumber.charAt(0) != '4'){ as it's checking the character instead of int.