example.java

import com.googlecode.javaewah.EWAHCompressedBitmap;

import java.io.*;
import java.nio.ByteBuffer;

/**
 * Simple illustrative example.
 * 
 * @author Daniel Lemire
 * 
 */
public class example
{

	/**
	 * @param args
	 *          arguments from the command line
	 * @throws IOException
	 *           if an IO error occurs
	 */
	public static void main(final String[] args) throws Exception {
		EWAHCompressedBitmap ewahBitmap1 = EWAHCompressedBitmap.bitmapOf(0, 2, 55,
				64, 1 << 30);
		EWAHCompressedBitmap ewahBitmap2 = EWAHCompressedBitmap.bitmapOf(1, 3, 64,
				1 << 30);
		System.out.println("bitmap 1: " + ewahBitmap1);
		System.out.println("bitmap 2: " + ewahBitmap2);
		// or
		EWAHCompressedBitmap orbitmap = ewahBitmap1.or(ewahBitmap2);
		System.out.println("bitmap 1 OR bitmap 2: " + orbitmap);
		System.out.println("memory usage: " + orbitmap.sizeInBytes() + " bytes");
		// and
		EWAHCompressedBitmap andbitmap = ewahBitmap1.and(ewahBitmap2);
		System.out.println("bitmap 1 AND bitmap 2: " + andbitmap);
		System.out.println("memory usage: " + andbitmap.sizeInBytes() + " bytes");
		// xor
		EWAHCompressedBitmap xorbitmap = ewahBitmap1.xor(ewahBitmap2);
		System.out.println("bitmap 1 XOR bitmap 2:" + xorbitmap);
		System.out.println("memory usage: " + xorbitmap.sizeInBytes() + " bytes");
		// fast aggregation over many bitmaps
		EWAHCompressedBitmap ewahBitmap3 = EWAHCompressedBitmap.bitmapOf(5, 55,
				1 << 30);
		EWAHCompressedBitmap ewahBitmap4 = EWAHCompressedBitmap.bitmapOf(4, 66,
				1 << 30);
		System.out.println("bitmap 3: " + ewahBitmap3);
		System.out.println("bitmap 4: " + ewahBitmap4);
		andbitmap = EWAHCompressedBitmap.and(ewahBitmap1, ewahBitmap2, ewahBitmap3,
				ewahBitmap4);
		System.out.println("b1 AND b2 AND b3 AND b4: " + andbitmap);
		// serialization
		ByteArrayOutputStream bos = new ByteArrayOutputStream();
		// Note: you could use a file output steam instead of ByteArrayOutputStream
		ewahBitmap1.serialize(new DataOutputStream(bos));
		EWAHCompressedBitmap ewahBitmap1new = new EWAHCompressedBitmap();
		byte[] bout = bos.toByteArray();
		ewahBitmap1new.deserialize(new DataInputStream(new ByteArrayInputStream(
				bout)));
		System.out.println("bitmap 1 (recovered) : " + ewahBitmap1new);
		if (!ewahBitmap1.equals(ewahBitmap1new))
			throw new RuntimeException("Will not happen");
		//
		// we can use a ByteBuffer as backend for a bitmap
		// which allows memory-mapped bitmaps
		//
		ByteBuffer bb = ByteBuffer.wrap(bout);
		EWAHCompressedBitmap rmap = new EWAHCompressedBitmap(bb);
		System.out.println("bitmap 1 (mapped) : " + rmap);

		if (!rmap.equals(ewahBitmap1))
			throw new RuntimeException("Will not happen");
		//
		// support for threshold function (new as of version 0.8.0):
		// mark as true a bit that occurs at least T times in the source
		// bitmaps
		//
		EWAHCompressedBitmap threshold2 = EWAHCompressedBitmap.threshold(2,
				ewahBitmap1, ewahBitmap2, ewahBitmap3, ewahBitmap4);
		System.out.println("threshold 2 : " + threshold2);

	}

}