From 4a85b01b386ffd47bb6aaddbe086e45413751d62 Mon Sep 17 00:00:00 2001
From: Looly <loolly@gmail.com>
Date: Thu, 23 Mar 2023 22:29:39 +0800
Subject: [PATCH] fix bug

---
 .../cn/hutool/core/date/CalendarUtil.java     | 27 +++++++++++++------
 .../cn/hutool/core/date/Issue3011Test.java    | 23 ++++++++++++++++
 2 files changed, 42 insertions(+), 8 deletions(-)
 create mode 100644 hutool-core/src/test/java/cn/hutool/core/date/Issue3011Test.java

diff --git a/hutool-core/src/main/java/cn/hutool/core/date/CalendarUtil.java b/hutool-core/src/main/java/cn/hutool/core/date/CalendarUtil.java
index 6c042e540..7ade9f387 100644
--- a/hutool-core/src/main/java/cn/hutool/core/date/CalendarUtil.java
+++ b/hutool-core/src/main/java/cn/hutool/core/date/CalendarUtil.java
@@ -358,6 +358,7 @@ public class CalendarUtil {
 	}
 	// endregion
 
+	// region ----- isSame
 	/**
 	 * 比较两个日期是否为同一天
 	 *
@@ -366,12 +367,7 @@ public class CalendarUtil {
 	 * @return 是否为同一天
 	 */
 	public static boolean isSameDay(final Calendar cal1, final Calendar cal2) {
-		if (cal1 == null || cal2 == null) {
-			throw new IllegalArgumentException("The date must not be null");
-		}
-		return cal1.get(Calendar.DAY_OF_YEAR) == cal2.get(Calendar.DAY_OF_YEAR) && //
-				cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR) && //
-				cal1.get(Calendar.ERA) == cal2.get(Calendar.ERA);
+		return isSameYear(cal1, cal2) && cal1.get(Calendar.DAY_OF_YEAR) == cal2.get(Calendar.DAY_OF_YEAR);
 	}
 
 	/**
@@ -409,7 +405,8 @@ public class CalendarUtil {
 	}
 
 	/**
-	 * 比较两个日期是否为同一月
+	 * 比较两个日期是否为同一月<br>
+	 * 同一个月的意思是：ERA（公元）、year（年）、month（月）都一致。
 	 *
 	 * @param cal1 日期1
 	 * @param cal2 日期2
@@ -417,11 +414,24 @@ public class CalendarUtil {
 	 * @since 5.4.1
 	 */
 	public static boolean isSameMonth(final Calendar cal1, final Calendar cal2) {
+		return isSameYear(cal1, cal2) && cal1.get(Calendar.MONTH) == cal2.get(Calendar.MONTH);
+	}
+
+	/**
+	 * 比较两个日期是否为同一年r>
+	 * 同一个月的意思是：ERA（公元）、year（年）都一致。
+	 *
+	 * @param cal1 日期1
+	 * @param cal2 日期2
+	 * @return 是否为同一年
+	 */
+	public static boolean isSameYear(final Calendar cal1, final Calendar cal2) {
 		if (cal1 == null || cal2 == null) {
 			throw new IllegalArgumentException("The date must not be null");
 		}
 		return cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR) && //
-				cal1.get(Calendar.MONTH) == cal2.get(Calendar.MONTH);
+				// issue#3011@Github
+				cal1.get(Calendar.ERA) == cal2.get(Calendar.ERA);
 	}
 
 	/**
@@ -444,6 +454,7 @@ public class CalendarUtil {
 
 		return date1.getTimeInMillis() == date2.getTimeInMillis();
 	}
+	// endregion
 
 	/**
 	 * 获得指定日期年份和季度<br>
diff --git a/hutool-core/src/test/java/cn/hutool/core/date/Issue3011Test.java b/hutool-core/src/test/java/cn/hutool/core/date/Issue3011Test.java
new file mode 100644
index 000000000..d28f81f76
--- /dev/null
+++ b/hutool-core/src/test/java/cn/hutool/core/date/Issue3011Test.java
@@ -0,0 +1,23 @@
+package cn.hutool.core.date;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.Calendar;
+
+public class Issue3011Test {
+	@Test
+	public void isSameMonthTest() {
+		// https://github.com/dromara/hutool/issues/3011
+		// 判断是否同一个月，还需考虑公元前和公元后的的情况
+		// 此处公元前2020年和公元2021年返回年都是2021
+		final Calendar calendar1 = Calendar.getInstance();
+		calendar1.set(-2020, Calendar.FEBRUARY, 12);
+
+		final Calendar calendar2 = Calendar.getInstance();
+		calendar2.set(2021, Calendar.FEBRUARY, 12);
+
+
+		Assert.assertFalse(DateUtil.isSameMonth(calendar1, calendar2));
+	}
+}