package collections;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;

public class MaxOccurrance {
 
    // this method takes the list argument
	public static int maxOccurrences(List<Integer> list) {
       
        // we use hashmap to store the element as key and number of times it repeats in 
        // in value, and finally return key which has the max value(i.e, most times it          
        // repeated
HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();

     // set the mode to 0 initilally
		int mode = 0;

		for (int key : list) {
			if (map.containsKey(key)) {
				map.put(key, map.get(key) + 1);
			} else
				map.put(key, 1);

             // updates the mode value for every iterate
			if (map.get(key) > mode)
				mode = map.get(key);
		}

		return mode;

	}

	public static void main(String args[]) {
		List<Integer> list = new ArrayList<Integer>();
		Collections.addAll(list, 5,5, 6, 2, 8, 8, 4, 5, 2, 4, 21, 7, 0, 6, 54, 2, 5, 8, 6);
		System.out.println("Number of times the most frequent occured integer is: " +maxOccurrences(list));
	}

}

Output:

Number of times the most frequent occured integer is: 4