import java.util.*;
import java.lang.*;
import java.io.*;
class GFG {
    
    public static void firstnonrepeatingcharacterinstream(char[] stream) {
        HashMap<Character,Integer> h = new HashMap<>();
        Queue<Character> q = new LinkedList<>();
        for(int i = 0; i < stream.length; i++) {
            h.put(stream[i], h.getorDefault(stream[i], 0) + 1);
            if(h.get(stream[i])==1) {
                q.add(stream[i]);
            }
        }
       
        while(!q.isEmpty()) {
            char c = q.peek();
            if(h.get(c) == 1) {
                break;
            } else {
                q.remove();
            }
        }
        if(q.isEmpty()) {
            System.out.print(-1 + "");
        } else {
            System.out.print(q.peek() + "");
        }
    }
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		
        int T = sc.nextInt();
		
        while (T-- > 0) {
		    int N=sc.nextInt();
		    char stream[]=new char[N];
            for(int i = 0; i < N; i++) {
                stream[i]=sc.next();
            }
			firstnonrepeatingcharacterinstream(stream);
        }
    }
}

Compilation Error
prog.java:12: error: cannot find symbol
h.put(stream[i],h.getorDefault(stream[i],0)+1);
^
symbol:   method getorDefault(char,int)
location: variable h of type HashMap<Character,Integer>
1 error

prog.java:12: error: cannot find symbol
h.put(stream[i],h.getorDefault(stream[i],0)+1); 

h.put(stream[i],h.getOrDefault(stream[i],0)+1);

char c=q.peek();

stream[i]=sc.next();