Java HashMap not finding key, but it should

Question

I have a strange issue occuring in my application, I will quickly explain global architecture and then my problem in depth.

I use a service to populate a HashM

Answer 1

map.get(do) returning null could be easily explained by assuming that the Boolean value for that key might be null but map.containsKey(do) returning false would require do's hashCode to be different at the time of calling containsKey(do) to it's hashCode at the time of retrieving it from the keySet.

To see what's happening, you could (temporarily) use a more verbose implementation of HashMap... Maybe something like this:

public class VerboseHashMap implements Map {

    private transient final static Logger logger = Logger.getLogger(VerboseHashMap.class);
    private HashMap internalMap = new HashMap();

    public boolean containsKey(Object o) {
        logger.debug("Object HashCode: " + o.hashCode());
        logger.debug("Map contents:");
        for (Entry entry : internalMap.entrySet()) {
            logger.debug(entry.getKey().hashCode() + " - " + entry.getValue().toString());
        }
        return internalMap.containsKey(o);
    }

    public V get(Object key) {
        logger.debug("Object HashCode: " + key.hashCode());
        logger.debug("Map contents:");
        for (Entry entry : internalMap.entrySet()) {
             logger.debug(entry.getKey().hashCode() + " - " + entry.getValue().toString());
        }
        return internalMap.get(key);
    }

}

You'd need to map all the other requirements of the Map interface to your internalMap as well.

Note: This code is not intended for production, nor is it in any way performance oriented, nice or unsmelly....

2nd note (after seeing your code): To use your domain-object as a key for your hashMap, you should only use the immutable parts of your object for hashCode and equals (in this case the id-value). Else lazy-loading further values would change the hashCode...

In Response to your comment:

public class Demo extends TestCase {

public void testMap() {

    Map map = new HashMap();
    DomainObject sb = new DomainObject();
    map.put(sb, "Some value");
    System.out.println(map.containsKey(sb));
    sb.value = "Some Text";
    System.out.println(map.containsKey(sb));

}

    private static class DomainObject {

        public String value = null;

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

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

    }

}

prints

true 
false

The HashCode for the key is computed at the time of putting it into the map.