Check out example codes for "calculating the percentile in java". It will help you in understanding the concepts better.

Code Example 1

/**
 * A simple method to log 95th percentile information
 */
private static void logPercentileInfo() {

    double total = 0;
    for (Map.Entry<Long, Long> entry : CassandraTimer.histogram.entrySet()) {
        long value = entry.getKey() * entry.getValue();
        total += value;
    }

    double sum = 0.95*total;

    double totalSum = 0;

    SortedSet<Long> keys = new TreeSet<Long>(CassandraTimer.histogram.keySet());
    for (long key : keys) {

        totalSum += CassandraTimer.histogram.get(key);

        if(totalSum >= sum) {
           //this is the 95th percentile I guess
            System.out.println(key);
        }
    }

}

Code Example 2

for (i=0, sum=0; i<n; i++) sum += Number[i];
tot = sum;
for (i=0, sum=0; i<n && sum < 0.95*tot; i++) sum += Number[i];
// i is about it

Code Example 3

public static long[] percentiles(long[] latencies, double... percentiles) {
    Arrays.sort(latencies, 0, latencies.length);
    long[] values = new long[percentiles.length];
    for (int i = 0; i < percentiles.length; i++) {
      int index = (int) (percentiles[i] * latencies.length);
      values[i] = latencies[index];
    }
    return values;
  }

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