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How to find repeated element count in a collection?


The java.util.Collections class consists exclusively of static methods that operate on or return collections. It contains polymorphic algorithms that operate on collections, “wrappers”, which return a new collection backed by a specified collection, and a few other odds and ends.

Collections.frequency() method will returns the number of elements in the specified collection equal to the specified object.
Syntax: public static int frequency(Collection c, Object o)

Example

package com.codesjava;
 
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
 
public class Test { 
    public static void main(String a[]){         
        List<String> list = new ArrayList<String>();
        list.add("vikas");
        list.add("ajay");
        list.add("mahesh");
        list.add("anil");
        list.add("vikas");
        list.add("anil");
        list.add("anil");
        list.add("mahesh");
        System.out.println("Actual list: "+list);
        System.out.println("Frequency of 'vikas': "+Collections.frequency(list, "vikas"));
        System.out.println("Frequency of 'ajay': "+Collections.frequency(list, "ajay"));
        System.out.println("Frequency of 'mahesh': "+Collections.frequency(list, "mahesh"));
        System.out.println("Frequency of 'anil': "+Collections.frequency(list, "anil"));
    }
}

Output

Actual list: [vikas, ajay, mahesh, anil, vikas, anil, anil, mahesh]
Frequency of 'vikas': 2
Frequency of 'ajay': 1
Frequency of 'mahesh': 2
Frequency of 'anil': 3

Java Collections class examples

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