1Z0-809 Question #207: Real Exam Question with Answer & Explanation

Given:

public interface LengthValidator {
 public boolean checkLength(String str);
}

and

public class Txt {
 public static void main(String[] args) {
 boolean res = new LengthValidator() {
 public boolean checkLength(String str) {
 return str.length() > 5 && str.length() < 10;
 }
 }.checkLength("Hello");
 }
}

Which interface from the java.util.function package should you use to refactor the class Txt?