title: How to put ArrayList object to parameter on getParam
body: <p>I'm using volley library and want to put <code>ArrayList</code> type of object on parameter.
  but on public <code>Map&lt;String, String&gt; getParams()</code>, I have to put String type.</p>
  
  <p>If i use int or other type, I can convert to String type using <code>String.valueOf(value)</code> methods, but I don't know how to convert in case the type is <code>ArrayList</code>.</p>
  
  <pre><code>public void putParam(String key, Object value) {
      if (value != null) {
          params.put(key, String.valueOf(value));
      } else {
          params.put(key, "");
      }
  }
  
  @Override
  public Map&lt;String, String&gt; getParams() {
  
      return params;
  }
  </code></pre>
  
  <p>I always fail if I put <code>ArrayList&lt;String&gt;</code> type, because server detect <code>ArrayList</code> type object as String type.</p>