Hyper Log Log Sketch Java Example

import java.io.FileInputStream;
import java.io.FileOutputStream;
import org.apache.datasketches.memory.Memory;
import org.apache.datasketches.hll.HllSketch;
import org.apache.datasketches.hll.TgtHllType;
import org.apache.datasketches.hll.Union;

// simplified file operations and no error handling for clarity
public class HllExample {

  public static void main(String[] args) throws Exception {
    final int lgK = 10;

    // this section generates two sketches with some overlap and serializes them into files
    {
      // 100000 unique keys
      HllSketch sketch1 = new HllSketch(lgK);
      for (int key = 0; key < 100000; key++) sketch1.update(key);
      FileOutputStream out1 = new FileOutputStream("HllSketch1.bin");
      out1.write(sketch1.toCompactByteArray());
      out1.close();

      // 100000 unique keys
      HllSketch sketch2 = new HllSketch(lgK);
      for (int key = 50000; key < 150000; key++) sketch2.update(key);
      FileOutputStream out2 = new FileOutputStream("HllSketch2.bin");
      out2.write(sketch2.toCompactByteArray());
      out2.close();
    }

    // this section deserializes the sketches, produces union and prints the results
    {
      FileInputStream in1 = new FileInputStream("HllSketch1.bin");
      byte[] bytes1 = new byte[in1.available()];
      in1.read(bytes1);
      in1.close();
      HllSketch sketch1 = HllSketch.heapify(Memory.wrap(bytes1));

      FileInputStream in2 = new FileInputStream("HllSketch2.bin");
      byte[] bytes2 = new byte[in2.available()];
      in2.read(bytes2);
      in2.close();
      HllSketch sketch2 = HllSketch.heapify(Memory.wrap(bytes2));

      Union union = new Union(lgK);
      union.update(sketch1);
      union.update(sketch2);
      HllSketch unionResult = union.getResult(TgtHllType.HLL_4);

      // debug summary of the union result sketch
      System.out.println(unionResult.toString());

      System.out.println("Union unique count estimate: " + unionResult.getEstimate());
      System.out.println("Union unique count lower bound 95% confidence: " + unionResult.getLowerBound(2));
      System.out.println("Union unique count upper bound 95% confidence: " + unionResult.getUpperBound(2));
    }
  }
}

Output:
### HLL SKETCH SUMMARY: 
Log Config K   : 10
Hll Target     : HLL_4
Current Mode   : HLL
LB             : 146594.82219597755
Estimate       : 151359.15391734682
UB             : 156443.56994041015
OutOfOrder Flag: true
CurMin         : 5
NumAtCurMin    : 12
HipAccum       : 146853.05495683785

Union unique count estimate: 151359.15391734682
Union unique count lower bound 95% confidence: 142121.27128389373
Union unique count upper bound 95% confidence: 161881.44803994312