org.apache.cassandra.utils
Class ReducingIterator<T1,T2>

java.lang.Object
  com.google.common.collect.UnmodifiableIterator<T>
      com.google.common.collect.AbstractIterator<T2>
          org.apache.cassandra.utils.ReducingIterator<T1,T2>

All Implemented Interfaces:

java.lang.Iterable<T2>, java.util.Iterator<T2>

Direct Known Subclasses:

CompactionIterator

public abstract class ReducingIterator<T1,T2>
extends com.google.common.collect.AbstractIterator<T2>
implements java.util.Iterator<T2>, java.lang.Iterable<T2>

reduces equal values from the source iterator to a single (optionally transformed) instance.

Field Summary

protected T1	last
protected java.util.Iterator<T1>	source

Constructor Summary

ReducingIterator(java.util.Iterator<T1> source)

Method Summary

protected T2	computeNext()
protected abstract T2	getReduced() return the last object computed by reduce
protected boolean	isEqual(T1 o1, T1 o2) override this if the keys you want to base the reduce on are not the same as the object itself (but can be generated from it)
java.util.Iterator<T2>	iterator()
protected void	onKeyChange() Called at the begining of each new key, before any reduce is called.
abstract void	reduce(T1 current) combine this object with the previous ones.

Methods inherited from class com.google.common.collect.AbstractIterator

endOfData, hasNext, next, peek

Methods inherited from class com.google.common.collect.UnmodifiableIterator

remove

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Iterator

hasNext, next, remove

Field Detail

source

protected java.util.Iterator<T1> source

last

protected T1 last

Constructor Detail

ReducingIterator

public ReducingIterator(java.util.Iterator<T1> source)

Method Detail

reduce

public abstract void reduce(T1 current)

combine this object with the previous ones. intermediate state is up to your implementation.

getReduced

protected abstract T2 getReduced()

return the last object computed by reduce

isEqual

protected boolean isEqual(T1 o1,
                          T1 o2)

override this if the keys you want to base the reduce on are not the same as the object itself (but can be generated from it)

computeNext

protected T2 computeNext()

Specified by:

computeNext in class com.google.common.collect.AbstractIterator<T2>

onKeyChange

protected void onKeyChange()

Called at the begining of each new key, before any reduce is called. To be overriden by implementing classes.

iterator

public java.util.Iterator<T2> iterator()

Specified by:

iterator in interface java.lang.Iterable<T2>