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>