Is there a way determine how many times an Object occurs within a Collection?

Created Aug 16, 2005

Brandon Rohlfs

The Collections class provides a method which returns the number of times an Object appears within a given Collection.

public static int frequency(Collection<?> c, Object o)

If a null Collection is passed in then a NullPointerException is thrown.

import java.util.*; 

public class Freq {
 public static void main(String[] args){
  List<Integer> password = new ArrayList<Integer>(); 
  password.add(new Integer(4));
  password.add(new Integer(6));
  password.add(new Integer(8));
  password.add(new Integer(4));
  password.add(new Integer(9));
  Integer passwordelement = new Integer(4); 
  System.out.println(passwordelement + " appears "
    + getFrequency(password,passwordelement) + " times within password"); 
 }
 private static int getFrequency(Collection c, Object o){
  return(Collections.frequency(c,o)); 
 }
}