TIOBE - Java Coding Standard

Rule: TypeResolution1

Synopsis:	Avoid using implementation types; use the interface instead
Language:	Java
Severity Level:	3
Category:	TypeResolution

Description:

Avoid using implementation types (i.e., HashSet); use the interface (i.e, Set) instead

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();
 }
}