How to Efficiently Count Substring Occurrences in Java?

Finding Occurrence of a Substring Within a String: Troubleshooting and an Alternative Solution

When executing the provided Java code to count occurrences of a substring within a string, you may encounter issues with the algorithm not halting. This issue stems from the constant increment of lastIndex without placing a check to ensure it doesn't exceed the bounds of the string str.

To resolve this issue, modify the code to include a conditional check that verifies if lastIndex is still within the bounds of str:

String str = "helloslkhellodjladfjhello";
String findStr = "hello";
int lastIndex = 0;
int count = 0;

while (lastIndex != -1 && lastIndex < str.length()) {
    lastIndex = str.indexOf(findStr, lastIndex);

    if (lastIndex != -1)
        count++;

    lastIndex += findStr.length();
}

System.out.println(count);

Alternatively, you can use the StringUtils.countMatches method from the Apache Commons Lang library:

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

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

This method simplifies the process of counting substring occurrences and ensures an efficient and reliable solution.

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