How to find a duplicate string in a string array

You have to change your code to :

public static void main(String args[]) {
        String arr[] = { "lady", "bird", "is", "bird", "lady", "cook" };
        int len = arr.length;
        System.out.println("Size " + len);
        for (int i = 0; i < len; i++) { // not <= but only <
            for (int j = i + 1; j < len; j++) {  // start from i+1 and go upto last element
                if (arr[i].equals(arr[j])) { // use equals()
                    System.out.println("Duplicate " + arr[i]);
                }
            }
        }
    }

O/P :

Size 6
Duplicate lady
Duplicate bird

Firsty Strings are to be compared with .equals() not ==

if(arr[i].equals(arr[j]))
{
   System.out.println("Duplicate "+arr[i]);
}

And I would recommend you to use sets as they dont allow duplicate values to be entered into it, or a list and check if it already exists using a .contains() method.

List<String> list = new ArrayList();

for(int i = 0; i < arr.length; i++)
   if(list.contains(arr[i])
     System.out.println("Duplicate" + arr[i]);
   else
     list.add(arr[i]); 

you can use a simpler approach like the following

Set<String> strings=new Hashset<String>();
for(int i=0;i<len;i++){
    if(strings.add(arr[i])==false){
        System.out.println(arr[i]+" is a duplicate");
    }
}

and in your existing code do it like arr[i].equals(arr[j]) to see if values are equal(if they are equal they are duplicate)

== checks for reference equivalence, while equals() method checks for value equivalence, so you should be using equals method whenever you need to check equivalence of two objects

hope it helps!

Good luck!

There are a few issues.

   for(int i=0 ; i<len;i++){
       for(int j=i +1 ; j< len;j++){
        if(arr[i].equals(arr[j])){
          System.out.println("Duplicate "+arr[i]);
      } 
   }  
       }

Note that: I have change j=1 to j=i and == to .equals and <= to < and len -1 to len

This gives you a list with the duplicates and their count:

var duplicates =
from word in arr
group word by word into g
where g.Count() > 1
select new { g.Key, Count = g.Count() };    

Create a Map of your words and occurencies.

import java.util.*;

public class TestDummy {
    public static void main(String args[]) {
        String arr[] = {
            "lady", "bird", "is", "bird", "lady", "cook"
        };
        Map<String, Integer> dictionary = new TreeMap<>();

        int len = arr.length;
        System.out.println("Size " + len);
        for (int i = 0; i < len; i++) {
            if (dictionary.containsKey(arr[i])) {
                dictionary.put(arr[i], dictionary.get(arr[i]) + 1);
                System.out.format("Duplicate %s%n", arr[i]);
            } else {
                dictionary.put(arr[i], 1);
            }
        }
    }
}



**Output**
    Size 6
    Duplicate bird
    Duplicate lady

public static String[] removeDuplicates(String[] array){                                           
    return new HashSet<String>(Arrays.asList(array)).toArray(new String[0]);       
}                                                                                   

above solutions does work
but just to make code clean you could use Linq.js