public static <T> void padLeft(List<T> list, int minLen, T padObj) {
		Objects.requireNonNull(list);
		if (list.isEmpty()) {
			padRight(list, minLen, padObj);
			return;
		}
		for (int i = list.size(); i < minLen; i++) {
			list.add(0, padObj);
		}
	}
@Test
	public void testPadLeft() {
		List<String> srcList = CollUtil.newArrayList();
		List<String> answerList = CollUtil.newArrayList("a", "b");
		CollUtil.padLeft(srcList, 1, "b");
		CollUtil.padLeft(srcList, 2, "a");
		assertEquals(srcList, answerList);

		srcList = CollUtil.newArrayList("a", "b");
		answerList = CollUtil.newArrayList("a", "b");
		CollUtil.padLeft(srcList, 2, "a");
		assertEquals(srcList, answerList);

		srcList = CollUtil.newArrayList("c");
		answerList = CollUtil.newArrayList("a", "a", "c");
		CollUtil.padLeft(srcList, 3, "a");
		assertEquals(srcList, answerList);
	}