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# 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