public abstract class AggregateWindow extends java.lang.Object implements java.io.Serializable
All custom java aggregate classes must extend AggregateWindow. The user's
subclass must implement at least one
accumulate method that corresponds to the argument number
and data types that a StreamBase expression (using calljava or its alias) refers to (typically used
in Aggregate and Query operators).
accumulate method will be called each time new data arrives for the window.
There may be many overloaded
accumulate methods, all with void return.
The user's subclass must also implement a
calculate method. When data is sent from
the aggregate window, The
calculate method must return a type matching a StreamBase
data type (for Strings you may also return byte, for blobs you must use
The return type may be the Java primitive or the Java Object which allows a null return type.
The calculate method will be called whenever a new tuple is generated. The calculate method may be called just once (as in the case when a tuple is generated when the aggregate window closes) or many times (as in the case when the aggregate window remains open, but a tuple is generated because "emit every N tuples" was selected).
It is also possible that calculate may be called before accumulate is called. It is also possible that calculate may never be called.
The AggregateWindow object is likely to be used several times. At the start of each new use, the init() method will be called. Then accumulate and calculate may be called. Finally, at the end of each use, release will be called.
Note: Serializations of instances of this class that are created (e.g., by using
ObjectOutputStream) in one version of StreamBase in general will not be
deserializable in any other version of StreamBase.
|Constructor and Description|
|Modifier and Type||Method and Description|
Called before each new use of this object.
Called after the end of a use of this object.
Called by internal streambase code to set the runtime environment
public abstract void init()
public void release()
public final void setRuntimeEnv(java.lang.Object env)
public final java.lang.Object getEnv()