java.util.Collections.frequency() method is present in java.util.Collections class. It is used to get the frequency of a element present in the specified list of Collection. More formally, it returns the number of elements e in the collection.
Syntax
public static int frequency(Collection<?> c, Object o) Parameters : c - the collection in which to determine the frequency of o o - the object whose frequency is to be determined Returns : Returns the number of elements in the specified collection equal to the specified object. Throws: NullPointerException - if c is null
// Java program to demonstrate working of // java.utils.Collections.frequency()  import java.util.*;   public class FrequencyDemo{    public static void main(String[] args)    {        // Let us create a list of strings        List<String> mylist = new ArrayList<String>();        mylist.add("practice");        mylist.add("code");        mylist.add("code");        mylist.add("quiz");        mylist.add("neveropen");           // Here we are using frequency() method        // to get frequency of element "code"        int freq = Collections.frequency(mylist, "code");           System.out.println(freq);    }} |
Output:
2
How to Quickly get frequency of an element in an array in Java ?
Arrays class in Java doesn’t have frequency method. But we can use Collections.frequency() to get frequency of an element in an array also.
// Java program to get frequency of an element // with java.utils.Collections.frequency()  import java.util.*;   public class FrequencyDemo{    public static void main(String[] args)    {        // Let us create an array of integers        Integer arr[] = {10, 20, 20, 30, 20, 40, 50};           // Please refer below post for details of asList()        // https://www.geeksforgeeks.org/array-class-in-java/        int freq = Collections.frequency(Arrays.asList(arr), 20);           System.out.println(freq);    }} |
Output:
3
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