I've discovered that overriding equals and hashcode should be done
with care. This might be obvious, but consider the following class:

public class Terminal {
       private String id;

       public Terminal() {
               this.id = "xz";
       }

       public Terminal(String id) {
               this.id = id;
       }

       @Override
       public boolean equals(Object obj) {
               if (this == obj)
                       return true;
               if (obj == null)
                       return false;
               if (getClass() != obj.getClass())
                       return false;
               Terminal other = (Terminal) obj;
               if (id == null) {
                       if (other.id != null)
                               return false;
               } else if (!id.equals(other.id))
                       return false;
               return true;
       }

       @Override
       public int hashCode() {
               final int prime = 31;
               int result = 1;
               result = prime * result + ((id == null) ? 0 : id.hashCode());
               return result;
       }
}

The equals method is the default eclipse implementation which also
compares the class (instead of doing instanceof). Running a simple
test:

public class ActiveObjectTest {
       @Test
       public void testActiveObjectCreation() {
               ActiveObject.newInstance(Terminal.class, 1000);
       }
}

Causes the following exception:

java.lang.NullPointerException
       at acterminals.Terminal$$ProxiedByAWSubclassing$$1266339987685.aw
$getAroundAdvice(Unknown Source)
       at acterminals.Terminal$$ProxiedByAWSubclassing$
$1266339987685_1_1984935277_147697296___AW_JoinPoint.invoke(Unknown
Source)
       at acterminals.Terminal$$ProxiedByAWSubclassing$
$1266339987685.hashCode(Unknown Source)
       at java.util.WeakHashMap.getEntry(WeakHashMap.java:378)
       at java.util.WeakHashMap.containsKey(WeakHashMap.java:369)
       at org.codehaus.aspectwerkz.aspect.DefaultMixinFactory.mixinOf
(DefaultMixinFactory.java:122)
       at org.codehaus.aspectwerkz.aspect.management.Mixins.mixinOf
(Mixins.java:147)
       at org.codehaus.aspectwerkz.aspect.management.Mixins.mixinOf
(Mixins.java:129)
       at acterminals.Terminal$$ProxiedByAWSubclassing$$1266339987685.<init>
(Unknown Source)
       at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native
Method)
       at sun.reflect.NativeConstructorAccessorImpl.newInstance
(NativeConstructorAccessorImpl.java:39)
       at sun.reflect.DelegatingConstructorAccessorImpl.newInstance
(DelegatingConstructorAccessorImpl.java:27)
       at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
       at java.lang.Class.newInstance0(Class.java:355)
       at java.lang.Class.newInstance(Class.java:308)
       at org.codehaus.aspectwerkz.proxy.ProxySubclassingStrategy.newInstance
(ProxySubclassingStrategy.java:88)
       at org.codehaus.aspectwerkz.proxy.Proxy.newInstance(Proxy.java:86)
       at se.scalablesolutions.akka.actor.ActiveObject$.newInstance
(ActiveObject.scala:186)
       at se.scalablesolutions.akka.actor.ActiveObject$.newInstance
(ActiveObject.scala:42)
       at se.scalablesolutions.akka.actor.ActiveObject.newInstance
(ActiveObject.scala)
       at acterminals.ActiveObjectTest.testActiveObjectCreation
(ActiveObjectTest.java:11)

Should hashcode and equals be implemented Scala-style instead?