I am parsing a xml file into a complex HashMap looking like this:

Map<String, Map<String, EcmObject>

EcmObject:

public class EcmObject implements Comparable, Serializable {
    private final EcmObjectType type;
    private final String name;
    private final List<EcmField> fields;
    private final boolean pages;

    // getter, equals, hashCode
}

EcmObjectType:

public enum EcmObjectType implements Serializable {
   FOLDER, REGISTER, DOCUMENT
}

EcmField

public class EcmField implements Comparable, Serializable {
    private final EcmFieldDataType dataType;
    private final EcmFieldControlType controlType;
    private final String name;
    private final String dbname;
    private final String internalname;
    private final Integer length;
    // getter, equals, hashCode
}

EcmFieldDataType

public enum EcmFieldDataType implements Serializable {
    TEXT, DATE, NUMBER, GROUP, DEC;
}

and EcmFieldControlType

public enum EcmFieldControlType implements Serializable{
    DEFAULT, CHECKBOX, LIST, DBLIST, TEXTAREA, HIERARCHY, TREE, GRID, RADIO, PAGECONTROL, STATIC;
}

I have overwritten all hashCode and equal methods by usind commons lang's EqualsBuilder and HashCodeBuilder. Now when I copy a A HashMap this way:

Map<String, Map<String, EcmObject>> m = EcmUtil.convertXmlObjectDefsToEcmEntries(new File("e:\\objdef.xml"));
Map<String, Map<String, EcmObject>> m2;

System.out.println(m.hashCode());

ByteArrayOutputStream baos = new ByteArrayOutputStream(8 * 4096);
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(m);
ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
ObjectInputStream ois = new ObjectInputStream(bais);

m2 = (Map<String, Map<String, EcmObject>>) ois.readObject();

System.out.println(m.hashCode());
System.out.println(m2.hashCode());

m.hashCode() is not equal to m2.hashCode()

here is my output:

-1639352210
-2071553208
1679930154

Another strange thing is, that eg. 10 times m has the same hashcode and suddenly on the 11th time the hashcode is different...

Any ideas what this is about?