Data update

Task/Factorial/Java/factorial-4.java

@@ -0,0 +1,27 @@
+import java.math.BigInteger;
+import java.util.function.Function;
+import java.util.stream.LongStream;
+import java.util.stream.Stream;
+
+public final class Factorial {
+
+	public static void main(String[] args) {
+		// Valid only for integer arguments 1, 2, ... , 20
+		Function<Integer, Long> factorialPositive = n -> LongStream.rangeClosed(2, n).reduce(1, (a, b) -> a * b);		
+		
+		// Valid for integer arguments <= 20
+		Function<Integer, Long> factorial = n -> {
+			if ( n < 0 || n > 20 ) {
+				throw new AssertionError("Argument is out of range: " + n);
+			}
+			
+			return factorialPositive.apply(n);
+		};
+		
+		// Return a BigInteger value
+		Function<Integer, BigInteger> factorialBig = n -> Stream.iterate(BigInteger.ONE, i -> i.add(BigInteger.ONE))
+				                                                .limit(n)
+				                                                .reduce(BigInteger.ONE, BigInteger::multiply);
+	}
+
+}