Add @SInCE tags to firstElement methods

Author: jhoeller

spring-core/src/main/java/org/springframework/util/CollectionUtils.java

@@ -314,84 +314,86 @@ else if (candidate != val.getClass()) {
 	}
 
 	/**
-	 * Retrieve the last element of the given Set, using {@link SortedSet#last()}
-	 * or otherwise iterating over all elements (assuming a linked set).
+	 * Retrieve the first element of the given Set, using {@link SortedSet#first()}
+	 * or otherwise using the iterator.
 	 * @param set the Set to check (may be {@code null} or empty)
-	 * @return the last element, or {@code null} if none
-	 * @since 5.0.3
+	 * @return the first element, or {@code null} if none
+	 * @since 5.2.3
 	 * @see SortedSet
 	 * @see LinkedHashMap#keySet()
 	 * @see java.util.LinkedHashSet
 	 */
 	@Nullable
-	public static <T> T lastElement(@Nullable Set<T> set) {
+	public static <T> T firstElement(@Nullable Set<T> set) {
 		if (isEmpty(set)) {
 			return null;
 		}
 		if (set instanceof SortedSet) {
-			return ((SortedSet<T>) set).last();
+			return ((SortedSet<T>) set).first();
 		}
 
-		// Full iteration necessary...
 		Iterator<T> it = set.iterator();
-		T last = null;
-		while (it.hasNext()) {
-			last = it.next();
+		T first = null;
+		if (it.hasNext()) {
+			first = it.next();
 		}
-		return last;
+		return first;
 	}
 
 	/**
-	 * Retrieve the last element of the given List, accessing the highest index.
+	 * Retrieve the first element of the given List, accessing the zero index.
 	 * @param list the List to check (may be {@code null} or empty)
-	 * @return the last element, or {@code null} if none
-	 * @since 5.0.3
+	 * @return the first element, or {@code null} if none
+	 * @since 5.2.3
 	 */
 	@Nullable
-	public static <T> T lastElement(@Nullable List<T> list) {
+	public static <T> T firstElement(@Nullable List<T> list) {
 		if (isEmpty(list)) {
 			return null;
 		}
-		return list.get(list.size() - 1);
+		return list.get(0);
 	}
 
 	/**
-	 * Retrieve the first element of the given Set, using {@link SortedSet#first()}
-	 * or otherwise using the iterator.
+	 * Retrieve the last element of the given Set, using {@link SortedSet#last()}
+	 * or otherwise iterating over all elements (assuming a linked set).
 	 * @param set the Set to check (may be {@code null} or empty)
-	 * @return the first element, or {@code null} if none
+	 * @return the last element, or {@code null} if none
+	 * @since 5.0.3
 	 * @see SortedSet
 	 * @see LinkedHashMap#keySet()
 	 * @see java.util.LinkedHashSet
 	 */
 	@Nullable
-	public static <T> T firstElement(@Nullable Set<T> set) {
+	public static <T> T lastElement(@Nullable Set<T> set) {
 		if (isEmpty(set)) {
 			return null;
 		}
 		if (set instanceof SortedSet) {
-			return ((SortedSet<T>) set).first();
+			return ((SortedSet<T>) set).last();
 		}
 
+		// Full iteration necessary...
 		Iterator<T> it = set.iterator();
-		T first = null;
-		if (it.hasNext()) {
-			first = it.next();
+		T last = null;
+		while (it.hasNext()) {
+			last = it.next();
 		}
-		return first;
+		return last;
 	}
 
 	/**
-	 * Retrieve the first element of the given List, accessing the zero index.
+	 * Retrieve the last element of the given List, accessing the highest index.
 	 * @param list the List to check (may be {@code null} or empty)
-	 * @return the first element, or {@code null} if none
+	 * @return the last element, or {@code null} if none
+	 * @since 5.0.3
 	 */
 	@Nullable
-	public static <T> T firstElement(@Nullable List<T> list) {
+	public static <T> T lastElement(@Nullable List<T> list) {
 		if (isEmpty(list)) {
 			return null;
 		}
-		return list.get(0);
+		return list.get(list.size() - 1);
 	}
 
 	/**