FirstNonRepeatChars.java

        /*  Find first non-repeated characters in given String */

import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;

public class FirstNonRepeatChars {

    public static void main(String[] args) {
        
        String input = "AABDBCCSDM";

        // First Approach without Collection

        for(int i=0; i<input.length(); i++) {
            
            boolean unique = true;

            for(int j=0; j<input.length(); j++) {
                if(i!=j && input.charAt(i) == input.charAt(j)) {
                    unique = false;
                    break;
                }
            }
            if(unique) {
                System.out.println(input.charAt(i));
                break;
            }
        }

        // Second Approach with Collection

        Map<Character, Integer> map = new HashMap();

        for(int i=0; i<input.length(); i++) {
            char ch = input.charAt(i);
            if(map.containsKey(ch)) {
                map.put(ch, map.get(ch)+1);
            }else {
                map.put(ch, 1);
            }
        }

        System.out.println(map);

        for(Entry<Character, Integer> entrySet : map.entrySet()) {
            if(entrySet.getValue() == 1) {
                System.out.println(entrySet.getKey());
                break;
            }
        }
    }
}