Avoid using implementation types (i.e., HashSet); use the interface (i.e, Set) instead Example:
<pre>
import java.util.ArrayList;
import java.util.HashSet;

public class Bar {

  // Use List instead
  private ArrayList list = new ArrayList();

  // Use Set instead
  public HashSet getFoo() {
    return new HashSet();
  }
}
</pre>

<p>
  This rule is deprecated, use {rule:squid:S1319} instead.
</p>