Add pattern matching example

lang/src/main/java/patternmatching/Statistics.java

@@ -0,0 +1,66 @@
+package patternmatching;
+
+import java.io.FileNotFoundException;
+import java.util.Arrays;
+import java.util.stream.Collectors;
+
+public final class Statistics {
+
+    private final long[] data;
+    private Double mean = null;
+    private Double variance = null;
+
+    private Statistics(long[] data) {
+        this.data = data;
+    }
+
+    double getMean() {
+        if (mean == null) {
+            mean = (double) Arrays.stream(data).sum() / data.length;
+        }
+
+        return mean;
+    }
+
+    double getVariance() {
+        if (variance == null) {
+            final double mean = getMean();
+            double temp = 0;
+            for(double a : data) {
+                temp += (a-mean)*(a-mean);
+            }
+            variance = temp/(data.length-1);
+        }
+
+        return variance;
+    }
+
+    double getStddev() {
+        return Math.sqrt(getVariance());
+    }
+
+    double getMedian() {
+        Arrays.sort(data);
+        if (data.length % 2 == 0) return (data[(data.length / 2) - 1] + data[data.length / 2]) / 2.0;
+        return data[data.length / 2];
+    }
+
+    static Statistics from(long[] data) {
+        return new Statistics(data);
+    }
+
+    @Override
+    public String toString() {
+        return String.format(
+                "mean=%.2fms stddev=%.2fms median=%.2fms",
+                getMean()/1000,
+                getStddev()/1000,
+                getMedian()/1000
+        );
+    }
+
+    public String asCSv() {
+        final String csv = Arrays.stream(data).mapToObj(String::valueOf).collect(Collectors.joining(","));
+        return csv;
+    }
+}