How to get the count of elements in an array? Duplicate Elements in array? Count of duplicate elements in array?Collection Interview Questions

This is one of the mostly asked interview question.

package CountElements;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

public class findduplicate {
    public static void main (String args[]) {
        String str2 = "findduplicateelementsinarray";
        String[] ary = str2.split("");
     ArrayList<String> list = new ArrayList<String>(Arrays.asList(ary));
 //Set does not allow duplicate elements
     Set<String> str1 = new HashSet<String>();{
     for ( String str21 : list) {
         if (str1.add(str21) == false) {
             System.out.println(str21 + " occurs: " + Collections.frequency(list, str21) +": is the Duplicate Element");
         }else if (Collections.frequency(list, str21) < 2) {
             System.out.println(str21 + " occurs: " + Collections.frequency(list, str21));
         }
     }
   
}}
}

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