Java.util.Collections.frequency() in Java with Examples

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("geeksforgeeks");
 
        // 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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