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.

  • Constructor Details

    • 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 Details

    • 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