From 043722e1da2079d1738823e1266f10b1b54838c9 Mon Sep 17 00:00:00 2001
From: asukavuuyn <1346007099@qq.com>
Date: Fri, 10 Oct 2025 00:12:05 +0800
Subject: [PATCH] =?UTF-8?q?fix:charAt=E8=B6=8A=E7=95=8C=E5=88=A4=E6=96=AD?=
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---
 .../src/main/java/cn/hutool/core/text/StrBuilder.java    | 2 +-
 .../test/java/cn/hutool/core/text/StrBuilderTest.java    | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/hutool-core/src/main/java/cn/hutool/core/text/StrBuilder.java b/hutool-core/src/main/java/cn/hutool/core/text/StrBuilder.java
index 305da2923..87e299f90 100644
--- a/hutool-core/src/main/java/cn/hutool/core/text/StrBuilder.java
+++ b/hutool-core/src/main/java/cn/hutool/core/text/StrBuilder.java
@@ -486,7 +486,7 @@ public class StrBuilder implements CharSequence, Appendable, Serializable {
 		if(index < 0){
 			index = this.position + index;
 		}
-		if ((index < 0) || (index > this.position)) {
+		if ((index < 0) || (index >= this.position)) {
 			throw new StringIndexOutOfBoundsException(index);
 		}
 		return this.value[index];
diff --git a/hutool-core/src/test/java/cn/hutool/core/text/StrBuilderTest.java b/hutool-core/src/test/java/cn/hutool/core/text/StrBuilderTest.java
index 474a71143..52f2d9222 100644
--- a/hutool-core/src/test/java/cn/hutool/core/text/StrBuilderTest.java
+++ b/hutool-core/src/test/java/cn/hutool/core/text/StrBuilderTest.java
@@ -131,4 +131,13 @@ public class StrBuilderTest {
 		helloWorld.insert(6, "Beautiful ");
 		Assertions.assertEquals("Hello Beautiful World", helloWorld.toString());
 	}
+
+	@Test
+	void charAtTest() {
+		final StrBuilder helloWorld = StrBuilder.create("Hello World");
+		Assertions.assertEquals(helloWorld.charAt(-1),'d');
+		Assertions.assertEquals(helloWorld.charAt(0),'H');
+		Assertions.assertEquals(helloWorld.charAt(10),'d');
+		Assertions.assertThrows(StringIndexOutOfBoundsException.class, () -> helloWorld.charAt(11));;
+	}
 }