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

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In this post, we will discuss and write Java program to count the number of occurrences of a substring in a String. 
Let's write a most efficient program with simple logic.

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.
package com.javaguides.strings.examples;

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

    public static void main(String[] args) {
        int count = countOccurrencesOf("javadevelopersguides", "java");
        System.out.println("Count number of occurrences of substring 'java' " +
            " in string 'javadevelopersguides' : " + count);
        int count1 = countOccurrencesOf("javajavaguides", "java");
        System.out.println("Count number of occurrences of substring 'java'" +
            "  in string 'javajavaguides' : " + 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;
    }
}
Output:
Count number of occurrences of substring 'java'  in string 'javadevelopersguides' : 1
Count number of occurrences of substring 'java'  in string 'javajavaguides' : 2
You can use this method as a common utility static method in your project work.
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