Thread: Index error

 
	public static void main(String[] args) throws IOException {
 
		ArrayList<String> listCliente = new ArrayList<>();
		ArrayList<String> listCliente1 = new ArrayList<>();
 
		BufferedReader reader = new BufferedReader(new FileReader("C:\\Users\\java\\Desktop\\prova.txt"));
		BufferedReader reader1 = new BufferedReader(new FileReader("C:\\Users\\java\\Desktop\\prova1.txt"));
 
		String line = reader.readLine();
        while(line!=null) {
            System.out.println(line);
            line = reader.readLine();
            listCliente.add(line);
        }
 
 
 
    	String line1 = reader1.readLine();
        while(line1!=null) {
            System.out.println(line1);
            line1 = reader1.readLine();
            listCliente1.add(line1);
        }
 
        System.out.println(listCliente);
        System.out.println(listCliente1);
 
 
 
		for (int i = 0; i < listCliente.size(); i++) {
			for (int j = 0; j < listCliente1.size(); j++) {
				if (listCliente.get(i).equals(listCliente1.get(j))) {
					System.out.println(listCliente.get(i));
				}
			}
		}
 
	}
 
}

Why do you give me an error?

output:
1
2
3
1
2
3
[2, 3, null]
[2, 3, null]
2
3
Exception in thread "main" java.lang.NullPointerException
at it.nexid.Test.main(Test.java:41)

both files have only three strings
1
2
3

Grazie