AggregatingIterator

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Class

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Deprecated

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org.jdaemon.util.iterator
Class AggregatingIterator

java.lang.Object
  org.jdaemon.util.iterator.AggregatingIterator

All Implemented Interfaces:: java.util.Iterator

public abstract class AggregatingIterator
extends java.lang.Object
implements java.util.Iterator

Abstract class for generating aggregate data from a collection

To create a concrete subclass of AggregatingIterator

beginGroup should be implemented to return a 'zero' value for aggregate data
addToGroup should be implemented to add a value from the underlying collection to the aggregate

For example, if beginGroup returns new Integer(0), and the underlying collection contains instances of a an employee class with name, department, and salary fields, addToGroup() could be implemented to add the salary from an employee object to the total.

Then if the Comparator object given to the AggregatingIterator sorts by the department field only, the resulting iterator will iterate over the total salary for all employees each department. Objects returned by the iterator will be map entries, where the key is the first employee object in each department, and the value is the value is the total salary for that department.

Field Summary

private java.util.Comparator comparator


private java.util.Iterator iterator


private java.util.Map.Entry next


Constructor Summary

AggregatingIterator(java.util.Collection collection, java.util.Comparator comparator, boolean sorted)
          Creates a new instance of AggregatingIterator

AggregatingIterator(java.util.Iterator iterator, java.util.Comparator comparator, boolean sorted)


AggregatingIterator(java.util.Map map, java.util.Comparator comparator, boolean sorted)


Method Summary

protected abstract java.lang.Object addToGroup(java.lang.Object group, java.lang.Object value)


protected abstract java.lang.Object beginGroup()


boolean hasNext()
          Tests whether there are elements remaining in the collection.

private static java.util.Map makeMap(java.util.Iterator i, java.util.Comparator comparator)


private static java.util.Map makeMap(java.util.Map old_map, java.util.Comparator comparator)


private void moveNext()


java.lang.Object next()
          Obtain the next element in the collection.

void remove()
          Remove from the underlying collection the last element returned by next (optional operation).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

iterator

private java.util.Iterator iterator

comparator

private java.util.Comparator comparator

private java.util.Map.Entry next

Constructor Detail