[java] Finding second occurrence of a substring in a string in Java

We are given a string, say, "itiswhatitis" and a substring, say, "is". I need to find the index of 'i' when the string "is" occurs a second time in the original string.

String.indexOf("is") will return 2 in this case. I want the output to be 10 in this case.

I hope I'm not late to the party.. Here is my answer. I like using Pattern/Matcher because it uses regex which should be more efficient. Yet, I think this answer could be enhanced:

    Matcher matcher = Pattern.compile("is").matcher("I think there is a smarter solution, isn't there?");
    int numOfOcurrences = 2;
    for(int i = 0; i < numOfOcurrences; i++) matcher.find();
    System.out.println("Index: " + matcher.start());

I am using: Apache Commons Lang: StringUtils.ordinalIndexOf()

StringUtils.ordinalIndexOf("Java Language", "a", 2)

i think a loop can be used.

1 - check if the last index of substring is not the end of the main string.
2 - take a new substring from the last index of the substring to the last index of the main string and check if it contains the search string
3 - repeat the steps in a loop

int first = string.indexOf("is");
int second = string.indexOf("is", first + 1);

This overload starts looking for the substring from the given index.

You can write a function to return array of occurrence positions, Java has String.regionMatches function which is quite handy

public static ArrayList<Integer> occurrencesPos(String str, String substr) {
    final boolean ignoreCase = true;
    int substrLength = substr.length();
    int strLength = str.length();

    ArrayList<Integer> occurrenceArr = new ArrayList<Integer>();

    for(int i = 0; i < strLength - substrLength + 1; i++) {
        if(str.regionMatches(ignoreCase, i, substr, 0, substrLength))  {
            occurrenceArr.add(i);
        }
    }
    return occurrenceArr;
}

if you want to find index for more than 2 occurrence:

public static int ordinalIndexOf(String fullText,String subText,int pos){

    if(fullText.contains(subText)){
        if(pos <= 1){
            return fullText.indexOf(subText);
        }else{
            --pos;
            return fullText.indexOf(subText, ( ordinalIndexOf(fullText,subText,pos) + 1) );
        }
    }else{
        return -1;
    }

}