How Can I Reliably Count Substring Occurrences in a String?

Count Substring Occurrences in a String

When attempting to ascertain the occurrences of a substring within a string, a common issue arises when the search algorithm fails to terminate. To rectify this, it is imperative to address the following:

Understanding the Issue

Consider the example provided, where the goal is to count occurrences of "hello" in the string "helloslkhellodjladfjhello." The algorithm iteratively searches for the substring using the indexOf method. However, it incrementally adjusts the lastIndex by the length of the substring, resulting in an infinite loop.

A Reliable Solution

To overcome this, one can employ the countMatches method from Apache Commons Lang. This predefined function accurately counts substring occurrences, as demonstrated in the code below:

String str = "helloslkhellodjladfjhello";
String findStr = "hello";

System.out.println(StringUtils.countMatches(str, findStr));

This yields the expected count of 3.

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