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java.util.Random in Java 8
package lambda;
import org.junit.Test;
import java.util.*;
import java.util.stream.*;
public class RandomStreamTest {
@Test
public void testRandomStream() {
Random random = new Random();
DoubleStream doubleStream = random.doubles(-1.0, 1.0);
LinkedHashMap<Range, Integer> rangeCountMap = doubleStream.limit(1000000)
.boxed()
.map(Ranges::of)
.collect(Ranges::emptyRangeCountMap, (m, e) -> m.put(e, m.get(e) + 1), Ranges::mergeRangeCountMaps);
rangeCountMap.forEach((k, v) -> System.out.println(k.from() + "\t" + v));
}
@Test
public void testGaussianRandomStream() {
Random random = new Random();
DoubleStream gaussianStream = Stream.generate(random::nextGaussian).mapToDouble(e -> e);
LinkedHashMap<Range, Integer> gaussianRangeCountMap =
gaussianStream
.filter(e -> (e >= -1.0 && e < 1.0))
.limit(1000000)
.boxed()
.map(Ranges::of)
.collect(Ranges::emptyRangeCountMap, (m, e) -> m.put(e, m.get(e) + 1), Ranges::mergeRangeCountMaps);
gaussianRangeCountMap.forEach((k, v) -> System.out.println(k.from() + "\t" + v));
}
public static class Range {
private final double from;
private final double to;
public Range(double from, double to) {
this.from = from;
this.to = to;
}
public double from() {
return from;
}
public double to() {
return to;
}
@Override
public String toString() {
return "From: " + from + " To: " + to;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Range range = (Range) o;
if (Double.compare(range.from, from) != 0) return false;
if (Double.compare(range.to, to) != 0) return false;
return true;
}
@Override
public int hashCode() {
int result;
long temp;
temp = Double.doubleToLongBits(from);
result = (int) (temp ^ (temp >>> 32));
temp = Double.doubleToLongBits(to);
result = 31 * result + (int) (temp ^ (temp >>> 32));
return result;
}
}
public static class Ranges {
private static LinkedHashMap<Integer, Range> rangeMap = new LinkedHashMap<>();
static {
rangeMap.put(-10, new Range(-1.0, -0.9));
rangeMap.put(-9, new Range(-0.9, -0.8));
rangeMap.put(-8, new Range(-0.8, -0.7));
rangeMap.put(-7, new Range(-0.7, -0.6));
rangeMap.put(-6, new Range(-0.6, -0.5));
rangeMap.put(-5, new Range(-0.5, -0.4));
rangeMap.put(-4, new Range(-0.4, -0.3));
rangeMap.put(-3, new Range(-0.3, -0.2));
rangeMap.put(-2, new Range(-0.2, -0.1));
rangeMap.put(-1, new Range(-0.1, 0.0 ));
rangeMap.put(0, new Range(0.0, 0.1 ));
rangeMap.put(1, new Range(0.1, 0.2 ));
rangeMap.put(2, new Range(0.2, 0.3 ));
rangeMap.put(3, new Range(0.3, 0.4 ));
rangeMap.put(4, new Range(0.4, 0.5 ));
rangeMap.put(5, new Range(0.5, 0.6 ));
rangeMap.put(6, new Range(0.6, 0.7 ));
rangeMap.put(7, new Range(0.7, 0.8 ));
rangeMap.put(8, new Range(0.8, 0.9 ));
rangeMap.put(9, new Range(0.9, 1.0 ));
}
public static Range of(double d) {
int key = (int) Math.floor(d * 10);
return rangeMap.get(key);
}
public static LinkedHashMap<Range, Integer> emptyRangeCountMap() {
LinkedHashMap<Range, Integer> rangeCountMap = new LinkedHashMap<>();
for (Range range : rangeMap.values()) {
rangeCountMap.put(range, 0);
}
return rangeCountMap;
}
public static void mergeRangeCountMaps(Map<Range, Integer> map1, Map<Range, Integer> map2) {
for (Range range : rangeMap.values()) {
map1.put(range, map1.get(range) + map2.get(range));
}
}
}
}
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