A CompositeData object associates string keys with the values of each data item. The CompositeDataSupport class defines an immutable map with an arbitrary number of entries, called data items, which can be of any type. To comply with the design patterns for open MBeans, all data items must have a type among the set of open MBean data types, including other CompositeData types.
When instantiating the CompositeDataSupport class, you must provide the description of the composite data object in a CompositeType object (see 4.1.2 Type Descriptor Classes). All the items provided through the constructor must match this description. Because the composite object is immutable, all items must be provided at instantiation time, and therefore the constructor can verify that the items match the description. The getOpenType method returns this description so that other objects which interact with a CompositeData object can know its structure.