forbid negafibonacci numbers

src/main/java/_12/_1/lukas/FibonacciDynamic.java

@@ -16,6 +16,9 @@ public class FibonacciDynamic extends Fibonacci {
 
 	@Override
 	public long calculate(int n) {
+		if(n < 0) {
+			throw new IllegalArgumentException("n must not be negative. Negafibonacci numbers are not supported.");
+		}
 		if(memory.containsKey(n)) {
 			return memory.get(n);
 		}

src/main/java/_12/_1/lukas/FibonacciParallelDynamic.java

@@ -15,6 +15,9 @@ public class FibonacciParallelDynamic extends Fibonacci {
 
 	@Override
 	public long calculate(int n) {
+		if(n < 0) {
+			throw new IllegalArgumentException("n must not be negative. Negafibonacci numbers are not supported.");
+		}
 		if(memory.containsKey(n)) {
 			return memory.get(n);
 		}

src/main/java/_12/_1/lukas/FibonacciParallelRecursive.java

@@ -5,6 +5,9 @@ import provided._12._1.Fibonacci;
 public class FibonacciParallelRecursive extends Fibonacci {
 	@Override
 	public long calculate(int n) {
+		if(n < 0) {
+			throw new IllegalArgumentException("n must not be negative. Negafibonacci numbers are not supported.");
+		}
 		if(n == 0 || n == 1) {
 			return n;
 		}

src/main/java/_12/_1/lukas/FibonacciRecursive.java

@@ -5,6 +5,9 @@ import provided._12._1.Fibonacci;
 public class FibonacciRecursive extends Fibonacci {
 	@Override
 	public long calculate(int n) {
+		if(n < 0) {
+			throw new IllegalArgumentException("n must not be negative. Negafibonacci numbers are not supported.");
+		}
 		if(n == 0 || n == 1) {
 			return n;
 		}