title: How to check if string contains only letters, numbers and double backslash
body: <p>How can I write a method to check if string contains <strong>only</strong> numbers, letters, specific characters (<code>+_-/</code>) and only double backslashes (<code>\\</code>).</p>
  
  <p>example:</p>
  
  <p><code>a2b/\</code>  - false</p>
  
  <p><code>d+sd\\ff</code> - true</p>
  
  <p>I tried this:</p>
  
  <pre><code>stringExample.matches("^[a-z-A-Z-0-9 +_-/]+");
  </code></pre>
  
  <p>...but it doesn't match a double backslash (<code>\\</code>).</p>