Java - How to Count the Number of Occurrences of Substring in a String

January 19, 2023

In this section, we will write a Java program to Count the Number of Occurrences of Substring in a String.

Java program to Count the Number of Occurrences of Substring in a String

In the below program, we have countOccurrencesOf(String str, String sub) a generic method, here we simply pass input string and substring as arguments and method return number of occurrences of the substring.

/**
 *
 * Java program to count number of occurrence of substring in given string.
 * @author knowledgefactory.net
 *
 */
public class Main {

    public static void main(String[] args) {

        int count = countOccurrencesOf("javaknowledgefactoryjava", "java");
        System.out.println("Count number of occurrences of substring 'java' " +
                " in string 'javaknowledgefactoryjava' : " + count);
        
        int count1 = countOccurrencesOf("javaknowledgefactoryjavajava", "java");
        System.out.println("Count number of occurrences of substring 'java'" +
                "  in string 'javaknowledgefactoryjavajava' : " + count1);
    }

    public static boolean hasLength(String str) {
        return (str != null && !str.isEmpty());
    }

    /**
     * Count the occurrences of the substring {@code sub} in string {@code str}.
     * @param str string to search in
     * @param sub string to search for
     */
    public static int countOccurrencesOf(String str, String sub) {
        if (!hasLength(str) || !hasLength(sub)) {
            return 0;
        }

        int count = 0;
        int pos = 0;
        int idx;
        while ((idx = str.indexOf(sub, pos)) != -1) {
            ++count;
            pos = idx + sub.length();
        }
        return count;
    }
}

Console Output:

Count number of occurrences of substring 'java'  in string 'javaknowledgefactoryjava' : 2
Count number of occurrences of substring 'java'  in string 'javaknowledgefactoryjavajava' : 3

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