I need help with an array

Question

Can anyone help me with this?
I keep getting two errors:
Cannot find symbol method "isEmpty()"
Cannot find symbol method "readString()"
import java.util.*;
import java.text.*;
import java.io.*;
import java.net.*;
import java.lang.*;
public class LetterCount3_1 {
public static void main(String[] args) {
int[] cnt = new int[26];
          InputStreamReader stdin = new InputStreamReader(System.in);
          BufferedReader console = new BufferedReader(stdin);
Scanner keyboard = new Scanner (System.in);
while (!stdin.isEmpty()) {
String s = stdin.readString();
for (int i = 0; i < 26; i++)
cnt[i] = 0;
for (int i = 0; i < s.length(); i++)
++cnt[s.charAt(i) - 'a'];
boolean match = true;
for (int i = 0; i < 26; i++)
if (cnt[i] != 0 && cnt[i] != 2) match = false;
if (match) System.out.println(s);
}

Answer 1

Thanks for that but now with this code the only problem I am getting is the isEmpty method.
import java.util.*;
import java.text.*;
import java.io.*;
import java.util.Scanner;
public class LetterCount3 {
    public static void main(String[] args) {
        int[] cnt = new int[26];      
          Scanner stdin = new Scanner(System.in);
        while (!stdin.isEmpty()) {
            String s = stdin.nextLine();
            for (int i = 0; i < 26; i++)
                cnt[i] = 0;
            for (int i = 0; i < s.length(); i++)
                ++cnt[s.charAt(i) - 'a'];
            boolean match = true;
            for (int i = 0; i < 26; i++)
                if (cnt[i] != 0 && cnt[i] != 2) match = false;
            if (match) System.out.println(s);
}