StringIndexOutOfBoundsException

Why This Happens

String methods like charAt(), substring(), and indexOf() throw this exception when the provided index is negative or exceeds the string length. This often happens when assuming a string has a minimum length without checking first.

The Problem

String text = "Hello";
char ch = text.charAt(10); // StringIndexOutOfBoundsException

The Fix

String text = "Hello";
if (text.length() > 10) {
    char ch = text.charAt(10);
}

Step-by-Step Fix

1. 1

   Identify the invalid index

   Read the exception message to find which index was out of range and check the actual string length.

2. 2

   Find the string operation

   Look at charAt(), substring(), or other string methods on the failing line to see which index argument is wrong.

3. 3

   Add length validation

   Check the string length before accessing by index, and handle the case where the string is shorter than expected.