Package org.roaringbitmap

Class IntIteratorFlyweight

java.lang.Object

org.roaringbitmap.IntIteratorFlyweight

All Implemented Interfaces:

Cloneable, IntIterator, PeekableIntIterator

public class IntIteratorFlyweight
extends Object
implements PeekableIntIterator

Fast iterator minimizing the stress on the garbage collector. You can create one reusable instance of this class and then wrap(RoaringBitmap) For better performance, consider the RoaringBitmap.forEach(org.roaringbitmap.IntConsumer) method.

Author:

Borislav Ivanov

Constructor Summary

Constructors

Constructor	Description
IntIteratorFlyweight()	Creates an instance that is not ready for iteration.
IntIteratorFlyweight(RoaringBitmap r)	Creates an instance that is ready for iteration.

Method Summary

Modifier and Type	Method	Description
void	advanceIfNeeded(int minval)	If needed, advance as long as the next value is smaller than minval The advanceIfNeeded method is used for performance reasons, to skip over unnecessary repeated calls to next.
PeekableIntIterator	clone()	Creates a copy of the iterator.
boolean	hasNext()
int	next()
int	peekNext()	Look at the next value without advancing The peek is useful when working with several iterators at once.
void	wrap(RoaringBitmap r)	Prepares a bitmap for iteration

Methods inherited from class java.lang.Object

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

Constructor Detail

IntIteratorFlyweight

public IntIteratorFlyweight()

Creates an instance that is not ready for iteration. You must first call wrap(RoaringBitmap).

IntIteratorFlyweight

public IntIteratorFlyweight(RoaringBitmap r)

Creates an instance that is ready for iteration.

Parameters:

r - bitmap to be iterated over

Method Detail

clone

public PeekableIntIterator clone()

Description copied from interface: PeekableIntIterator

Creates a copy of the iterator.

Specified by:

clone in interface IntIterator

Specified by:

clone in interface PeekableIntIterator

Overrides:

clone in class Object

Returns:

a clone of the current iterator

hasNext

public boolean hasNext()

Specified by:

hasNext in interface IntIterator

Returns:

whether there is another value

next

public int next()

Specified by:

next in interface IntIterator

Returns:

next integer value

wrap

public void wrap(RoaringBitmap r)

Prepares a bitmap for iteration

Parameters:

r - bitmap to be iterated over

advanceIfNeeded

public void advanceIfNeeded(int minval)

Description copied from interface: PeekableIntIterator

If needed, advance as long as the next value is smaller than minval The advanceIfNeeded method is used for performance reasons, to skip over unnecessary repeated calls to next. Suppose for example that you wish to compute the intersection between an ordered list of integers (e.g., int[] x = {1,4,5}) and a PeekableIntIterator. You might do it as follows...

     PeekableIntIterator j = // get an iterator
     int val = // first value from my other data structure
     j.advanceIfNeeded(val);
     while ( j.hasNext() ) {
       if(j.next() == val) {
         // ah! ah! val is in the intersection...
         // do something here
         val = // get next value?
       }
       j.advanceIfNeeded(val);
     }
     

The benefit of calling advanceIfNeeded is that each such call can be much faster than repeated calls to "next". The underlying implementation can "skip" over some data.

Specified by:

advanceIfNeeded in interface PeekableIntIterator

Parameters:

minval - threshold

peekNext

public int peekNext()

Description copied from interface: PeekableIntIterator

Look at the next value without advancing The peek is useful when working with several iterators at once. Suppose that you have 100 iterators, and you want to compute their intersections without materializing the result. You might do it as follows...

    PriorityQueue pq = new PriorityQueue(100,
      new Comparator<PeekableIntIterator>() {
             public int compare(PeekableIntIterator a,
                                PeekableIntIterator b) {
                 return a.peek() - b.peek();
             }
         });
 
    //...  populate pq
    
    while(! pq.isEmpty() ) {
      // get iterator with a smallest value
      PeekableIntIterator pi = pq.poll();
      int x = pi.next(); // advance
      // do something with x
      if(pi.hasNext()) pq.add(pi)
    }
    

Notice how the peek method allows you to compare iterators in a way that the next method could not do.

Specified by:

peekNext in interface PeekableIntIterator

Returns:

next value