Java - count duplicates in ArrayList

In this article, we would like to show you how to count duplicated elements in ArrayList in Java.

Quick solution:

int occurrences = Collections.frequency(myArrayList, element);

Practical example

In this example, we count the number of duplicated elements in letters ArrayList using Collections.frequency() method.

import java.util.*;

public class Example {

    public static void main(String[] args) {
        List<String> letters = new ArrayList<>();

        letters.add("A");
        letters.add("A");
        letters.add("A");

        letters.add("B");
        letters.add("B");

        letters.add("C");

        int occurrencesA = Collections.frequency(letters, "A");
        System.out.println("number of A element occurrences: " + occurrencesA);

        int occurrencesB = Collections.frequency(letters, "B");
        System.out.println("number of B element occurrences: " + occurrencesB);

        int occurrencesC = Collections.frequency(letters, "C");
        System.out.println("number of C element occurrences: " + occurrencesC);
    }
}

Output:

number of A element occurrences: 3
number of B element occurrences: 2
number of C element occurrences: 1