== Why is this an issue?

Just as you can't cut something into three halves, you can't grab a ``++substring++`` that starts or ends outside the original ``++String++``'s bounds, you can't use ``++substring++`` to get a reversed portion of a ``++String++``, and you can't get the ``++charAt++`` a value that's before the ``++String++`` starts or after it ends.


This rule detects when negative literal or ``++String::length++`` is passed as an argument to the ``++String::substring++``, ``++String::charAt++`` and related methods.


=== Noncompliant code example

[source,java]
----
String speech = "Now is the time for all good people to come to the aid of their country.";

String substr1 = speech.substring(-1, speech.length());  // Noncompliant; start and end values both bad
String substr2 = speech.substring(speech.length(), 0); // Noncompliant, start value must be < end value
char ch = speech.charAt(speech.length());  // Noncompliant
----


=== Compliant solution

[source,java]
----
String speech = "Now is the time for all good people to come to the aid of their country.";

String substr1 = speech; // Closest correct values to original code yield whole string
String substr2 = new StringBuilder(speech).reverse().toString()
char ch = speech.charAt(speech.length()-1);
----



ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Refactor this "[substring|charAt]" call; it will result in an "StringIndexOutOfBounds" exception at runtime.


'''
== Comments And Links
(visible only on this page)

=== relates to: S2121

endif::env-github,rspecator-view[]