Class ChunkStepper

java.lang.Object
uk.ac.starlink.array.ChunkStepper

public class ChunkStepper extends Object
Allows convenient stepping through an array. This class is provided as a convenience for applications code which wishes to iterate through an array in sections, at each stage obtaining a java primitive array containing a contiguous chunk of its pixels. This may be more efficient than using the single-element read/write methods of NDArray.

This class does not do anything very clever; it simply provides at each iteration base and length of a block which will take you from the start to the end of an array of given size over the lifetime of the iterator. These blocks will be of the same (user-defined or default) size with the possible exception of the last one, which will just mop up any remaining elements.

The simplest use of this class would therefore look something like this

     ArrayAccess acc = nda.getAccess(); 
     long npix = acc.getShape().getNumPixels();
     for ( ChunkStepper cIt = new ChunkStepper( npix ); 
           cIt.hasNext(); cIt.next() ) {
         int size = cIt.getSize();
         Object buffer = acc.getType().newArray( size );
         acc.read( buffer, 0, size );
         doStuff( buffer );
     }
 
A more efficient loop would reuse the same buffer array to save on object creation/collection costs as follows:
     ChunkStepper cIt = new ChunkStepper( npix );
     Object buffer = acc.getType().newArray( cIt.getSize() );
     for ( ; cIt.hasNext(); cIt.next() ) {
         acc.read( buffer, 0, cIt.getSize() );
         doStuff( buffer );
     }
 
The BufferIterator class provides very similar functionality in a way which may be slightly more convenient to use.
Version:
$Id$
Author:
Mark Taylor
See Also:
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static int
    The default size of chunks if not otherwise specified.
  • Constructor Summary

    Constructors
    Constructor
    Description
    ChunkStepper(long length)
    Create a new ChunkStepper with the default chunk size.
    ChunkStepper(long length, int chunkSize)
    Create a new ChunkStepper with a given chunk size.
  • Method Summary

    Modifier and Type
    Method
    Description
    long
    The offset of the base of the current chunk.
    int
    Get the size of the current chunk.
    long
    Returns the length of this ChunkStepper as supplied to the constructor - the total number of elements over which it will iterate.
    boolean
    See if iteration has finished.
    void
    Iterates to the next chunk.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
  • Field Details

    • defaultChunkSize

      public static int defaultChunkSize
      The default size of chunks if not otherwise specified.
  • Constructor Details

    • ChunkStepper

      public ChunkStepper(long length, int chunkSize)
      Create a new ChunkStepper with a given chunk size.
      Parameters:
      length - the total number of elements to iterate over
      chunkSize - the size of chunk which will be used (except perhaps for the last chunk)
      Throws:
      IllegalArgumentException - if chunkSize<=0 or length<0
    • ChunkStepper

      public ChunkStepper(long length)
      Create a new ChunkStepper with the default chunk size.
      Parameters:
      length - the total number of elements to iterate over
  • Method Details

    • hasNext

      public boolean hasNext()
      See if iteration has finished.
      Returns:
      true iff there are more chunks
    • getSize

      public int getSize()
      Get the size of the current chunk. It will be equal to the size specified in the constructor (or the default if none was specified), except for the last chunk, when it may be smaller.
      Returns:
      the current chunk size
    • getBase

      public long getBase()
      The offset of the base of the current chunk. Zero for the first chunk, and increasing by getSize with each iteration after that.
      Returns:
      the base of the current chunk
    • next

      public void next()
      Iterates to the next chunk.
      Throws:
      NoSuchElementException - if hasNext would return false
    • getTotalLength

      public long getTotalLength()
      Returns the length of this ChunkStepper as supplied to the constructor - the total number of elements over which it will iterate.