An attribute set contains a group of attribute values, where duplicate values are not allowed in the set. Furthermore, each value in an attribute set is a member of some category, and at most one value in any particular category is allowed in the set. For an attribute set, the values are Attribute objects, and the categories are Class objects. An attribute's category is the class (or interface) at the root of the class hierarchy for that kind of attribute. Note that an attribute object's category may be a superclass of the attribute object's class rather than the attribute object's class itself. An attribute object's category is determined by calling the getCategory() method defined in interface Attribute.

The interfaces of an AttributeSet resemble those of the Java Collections API's java.util.Map interface, but is more restrictive in the types it will accept, and combines keys and values into an Attribute.

Attribute sets are used in several places in the Print Service API. In each context, only certain kinds of attributes are allowed to appear in the attribute set, as determined by the tagging interfaces which the attribute class implements -- DocAttribute, PrintRequestAttribute, PrintJobAttribute, and PrintServiceAttribute. There are four specializations of an attribute set that are restricted to contain just one of the four kinds of attribute -- DocAttributeSet, PrintRequestAttributeSet, PrintJobAttributeSet, and PrintServiceAttributeSet, respectively. Note that many attribute classes implement more than one tagging interface and so may appear in more than one context.

• A DocAttributeSet, containing DocAttributes, specifies the characteristics of an individual doc and the print job settings to be applied to an individual doc.

• A PrintRequestAttributeSet, containing PrintRequestAttributes, specifies the settings to be applied to a whole print job and to all the docs in the print job.

• A PrintJobAttributeSet, containing PrintJobAttributes, reports the status of a print job.

• A PrintServiceAttributeSet, containing PrintServiceAttributes, reports the status of a Print Service instance.

In some contexts, the client is only allowed to examine an attribute set's contents but not change them (the set is read-only). In other places, the client is allowed both to examine and to change an attribute set's contents (the set is read-write). For a read-only attribute set, calling a mutating operation throws an UnmodifiableSetException.

The Print Service API provides one implementation of interface AttributeSet, class HashAttributeSet. A client can use class HashAttributeSet or provide its own implementation of interface AttributeSet. The Print Service API also provides implementations of interface AttributeSet's subinterfaces -- classes HashDocAttributeSet, HashPrintRequestAttributeSet, HashPrintJobAttributeSet, and HashPrintServiceAttributeSet.