feat: utility method for padding list

hutool-core/src/main/java/cn/hutool/core/collection/CollUtil.java

@@ -38,6 +38,7 @@ public class CollUtil {
 
 	/**
 	 * 填充List，以达到最小长度
+	 *
 	 * @param list 列表
 	 * @param minLen 最小长度
 	 * @param padObj 填充的对象
@@ -45,32 +46,26 @@ public class CollUtil {
 	 */
 	public static <T> void padLeft(List<T> list, int minLen, T padObj) {
 		Objects.requireNonNull(list);
-		if (isEmpty(list)) {
+		if (list.isEmpty()) {
 			padRight(list, minLen, padObj);
 			return;
 		}
-		int iterCnt = minLen - list.size();
-		if (iterCnt < 1) {
-			return;
-		}
-		List<T> padList = new ArrayList<>(iterCnt);
-		for (int i = 0; i < iterCnt; i++) {
-			padList.add(padObj);
+		for (int i = list.size(); i < minLen; i++) {
+			list.add(0, padObj);
 		}
-		list.addAll(0, padList);
 	}
 
 	/**
 	 * 填充List，以达到最小长度
+	 *
 	 * @param list 列表
 	 * @param minLen 最小长度
 	 * @param padObj 填充的对象
 	 * @param <T> 集合元素类型
 	 */
-	public static <T> void padRight(List<T> list, int minLen, T padObj) {
+	public static <T> void padRight(Collection<T> list, int minLen, T padObj) {
 		Objects.requireNonNull(list);
-		int iterCnt = minLen - list.size();
-		for (int i = 0; i < iterCnt; i++) {
+		for (int i = list.size(); i < minLen; i++) {
 			list.add(padObj);
 		}
 	}

hutool-core/src/test/java/cn/hutool/core/collection/CollUtilTest.java

@@ -21,28 +21,28 @@ public class CollUtilTest {
 
 	@Test
 	public void testPadLeft() {
-		List<Integer> srcList = CollUtil.newArrayList();
-		List<Integer> answerList = CollUtil.newArrayList(2, 1);
-		CollUtil.padLeft(srcList, 1, 1);
-		CollUtil.padLeft(srcList, 2, 2);
+		List<String> srcList = CollUtil.newArrayList();
+		List<String> answerList = CollUtil.newArrayList("a", "b");
+		CollUtil.padLeft(srcList, 1, "b");
+		CollUtil.padLeft(srcList, 2, "a");
 		Assert.assertEquals(srcList, answerList);
 
-		srcList = CollUtil.newArrayList(1, 2);
-		answerList = CollUtil.newArrayList(1, 2);
-		CollUtil.padLeft(srcList, 2, 1);
+		srcList = CollUtil.newArrayList("a", "b");
+		answerList = CollUtil.newArrayList("a", "b");
+		CollUtil.padLeft(srcList, 2, "a");
 		Assert.assertEquals(srcList, answerList);
 
-		srcList = CollUtil.newArrayList(3);
-		answerList = CollUtil.newArrayList(1, 1, 3);
-		CollUtil.padLeft(srcList, 3, 1);
+		srcList = CollUtil.newArrayList("c");
+		answerList = CollUtil.newArrayList("a", "a", "c");
+		CollUtil.padLeft(srcList, 3, "a");
 		Assert.assertEquals(srcList, answerList);
 	}
 
 	@Test
 	public void testPadRight() {
-		List<Integer> srcList = CollUtil.newArrayList(6);
-		List<Integer> answerList = CollUtil.newArrayList(6, 3, 3, 3, 3);
-		CollUtil.padRight(srcList, 5, 3);
+		List<String> srcList = CollUtil.newArrayList("a");
+		List<String> answerList = CollUtil.newArrayList("a", "b", "b", "b", "b");
+		CollUtil.padRight(srcList, 5, "b");
 		Assert.assertEquals(srcList, answerList);
 	}