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copied!<p>I don't know that I agree with the approach but you could do</p> <pre><code>enum CanDos { TALK, WALK, SLEEP, SIT, STARE } </code></pre> <p>And then the class could have</p> <pre><code>abstract class Foo { abstract Set<CanDos> getCanDos(); //or abstract boolean can(CanDos item); } </code></pre> <p>And you can use an <code>EnumSet</code> for efficient storage of the capabilities.</p> <p>If all you are looking for is the Right Thing to provide a set of enums (like the field in the parent abstract class you mention) then I think <a href="http://docs.oracle.com/javase/1.5.0/docs/api/java/util/EnumSet.html" rel="nofollow noreferrer"><code>EnumSet<CanDos></code></a> is your guy. In that case</p> <pre><code>abstract class Foo { private final Set<CanDos> candos; protected Foo(Set<CanDos> candos) { this.candos = new EnumSet<CanDos>(candos); } public boolean can(CanDos item) { return candos.contains(item); } } </code></pre> <p>Alternatively you could avoid the abstract class altogether (or at least not mandate it see e.g. <a href="https://stackoverflow.com/questions/1474249/abstract-classes-vs-interfaces">this question</a> or <a href="https://stackoverflow.com/questions/462198/java-interface-vs-abstract-class-regarding-fields">this one</a>). The well-regarded book <em>Effective Java</em> suggests "<a href="https://stackoverflow.com/questions/56867/interface-vs-base-class">Prefer interfaces to abstract classes</a>". </p> <p>To do this, instead </p> <pre><code>enum CanDos { TALK, WALK, SLEEP, SIT, STARE } public interface FooThatCanDo { boolean can(CanDos item); } </code></pre> <p>If you really think there's value in a common inheritance root (which you should think hard about) then you could provide an abstract base implementation as shown above, and declare that it <code>implements FooThatCanDo</code>. </p>

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