Get the first n elements of a List into an Array (#14599)

* Get the first n elements of a List into an Array

* [first-n-to-array] rename N -> n

core-java-modules/core-java-collections-conversions-2/src/test/java/com/baeldung/arrayconversion/ListToArrayFirstNElementsUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.arrayconversion;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import java.util.Iterator;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import com.google.common.collect.Lists;
+
+public class ListToArrayFirstNElementsUnitTest {
+    private static final List<String> INPUT_LIST = Lists.newArrayList("one", "two", "three", "four", "five", "six", "seven");
+    private static final int n = 5;
+
+    @Test
+    void whenUsingForLoop_thenGetExpectedArray() {
+        String[] result = new String[n];
+        for (int i = 0; i < n; i++) {
+            result[i] = INPUT_LIST.get(i);
+        }
+        assertArrayEquals(new String[] { "one", "two", "three", "four", "five" }, result);
+
+        String[] result2 = new String[n];
+        Iterator<String> iterator = INPUT_LIST.iterator();
+        for (int i = 0; i < n && iterator.hasNext(); i++) {
+            result2[i] = iterator.next();
+        }
+        assertArrayEquals(new String[] { "one", "two", "three", "four", "five" }, result2);
+    }
+
+    @Test
+    void whenUsingSubList_thenGetExpectedArray() {
+        String[] result = new String[n];
+        INPUT_LIST.subList(0, n)
+          .toArray(result);
+        assertArrayEquals(new String[] { "one", "two", "three", "four", "five" }, result);
+
+        String[] result2 = INPUT_LIST.subList(0, n)
+          .toArray(new String[0]);
+        assertArrayEquals(new String[] { "one", "two", "three", "four", "five" }, result2);
+
+        // available only for java 11+
+        String[] result3 = INPUT_LIST.subList(0, n)
+          .toArray(String[]::new);
+        assertArrayEquals(new String[] { "one", "two", "three", "four", "five" }, result3);
+    }
+
+    @Test
+    void whenUsingStream_thenGetExpectedArray() {
+        String[] result = INPUT_LIST.stream()
+          .limit(n)
+          .toArray(String[]::new);
+        assertArrayEquals(new String[] { "one", "two", "three", "four", "five" }, result);
+    }
+}