title: Java checking if string contains certain letters with a certain range with contains or equals method
body: <pre><code>import.java.util.Scanner;
  
  public class Test{
     public static void main(String[] args){
     Scanner sc = new Scanner(System.in)
     String operation = sc.nextLine();
     }
  }
  </code></pre>
  
  <p>When I want to see, if the string operation contains certain letters, I could write f.ex.</p>
  
  <pre><code>    if(operation.contains("a") || operation.contains("b")){
          System.out.println("This is not a valid choice. Please retry!");
      }
  </code></pre>
  
  <p>But I want to know what to write, if the string contains letters, e.g. from a to k. If I write it with || every single time, it's not efficient.
  EDIT: I'm only allowed to use the methods contains and equals.</p>