diff --git a/src/main/java/xyz/zhouxy/plusone/commons/annotation/ImmutableObject.java b/src/main/java/xyz/zhouxy/plusone/commons/annotation/ImmutableObject.java
deleted file mode 100644
index 5a8c51c..0000000
--- a/src/main/java/xyz/zhouxy/plusone/commons/annotation/ImmutableObject.java
+++ /dev/null
@@ -1,48 +0,0 @@
-/*
- * Copyright 2024 the original author or authors.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package xyz.zhouxy.plusone.commons.annotation;
-
-import java.lang.annotation.Target;
-
-import com.google.common.annotations.Beta;
-
-import java.lang.annotation.ElementType;
-import java.lang.annotation.Retention;
-import java.lang.annotation.RetentionPolicy;
-
-/**
- * 标记不可变对象。根据约定，该对象的字段只能是不可变对象或基础数据类型，且都是只读的。如：
- * <pre>@ImmutableObject
- * class Foo {
- *     private final @Getter int intVal;
- *     private final @Getter String stringVal;
- *     private final @Getter LocalDate dateVal;
- *     private final @Getter BigDecimal decimalVal;
- * }
- * </pre>
- * <p>
- * 如 guava 的 ImmutableList、ImmutableMap 等不可变集合，不属于此，因为其不要求包含的元素本身是不可变的。
- * <p>
- * 
- * @author <a href="http://zhouxy.xyz:3000/ZhouXY108">ZhouXY</a>
- * @since 0.1.0
- */
-@Beta
-@Target(ElementType.TYPE)
-@Retention(RetentionPolicy.RUNTIME)
-public @interface ImmutableObject {
-}
diff --git a/src/main/java/xyz/zhouxy/plusone/commons/math/Interval.java b/src/main/java/xyz/zhouxy/plusone/commons/math/Interval.java
index dbd3192..aed22e9 100644
--- a/src/main/java/xyz/zhouxy/plusone/commons/math/Interval.java
+++ b/src/main/java/xyz/zhouxy/plusone/commons/math/Interval.java
@@ -21,9 +21,11 @@ import java.util.Optional;
 import javax.annotation.Nonnull;
 
 import com.google.common.base.Preconditions;
+import com.google.errorprone.annotations.Immutable;
 
 import xyz.zhouxy.plusone.commons.util.Numbers;
 
+@Immutable
 public class Interval<T extends Comparable<T>> {
     @Nonnull
     private final IntervalType intervalType;
@@ -50,29 +52,29 @@ public class Interval<T extends Comparable<T>> {
     }
 
     @Nonnull
-    public IntervalType getIntervalType() {
+    public final IntervalType getIntervalType() {
         return intervalType;
     }
 
     @Nonnull
-    public Optional<T> getLowerBound() {
+    public final Optional<T> getLowerBound() {
         return Optional.ofNullable(lowerBound);
     }
 
     @Nonnull
-    public Optional<T> getUpperBound() {
+    public final Optional<T> getUpperBound() {
         return Optional.ofNullable(upperBound);
     }
 
-    public boolean isLeftClosed() {
+    public final boolean isLeftClosed() {
         return this.intervalType.isLeftClosed();
     }
 
-    public boolean isRightClosed() {
+    public final boolean isRightClosed() {
         return this.intervalType.isRightClosed();
     }
 
-    public boolean validValue(@Nonnull T value) {
+    public final boolean validValue(@Nonnull T value) {
         return Numbers.between(value, this.lowerBound, this.upperBound, this.intervalType);
     }
 }
diff --git a/src/main/java/xyz/zhouxy/plusone/commons/time/YearQuarter.java b/src/main/java/xyz/zhouxy/plusone/commons/time/YearQuarter.java
index c4c2a8d..7fc15a3 100644
--- a/src/main/java/xyz/zhouxy/plusone/commons/time/YearQuarter.java
+++ b/src/main/java/xyz/zhouxy/plusone/commons/time/YearQuarter.java
@@ -29,12 +29,14 @@ import java.util.Objects;
 import javax.annotation.Nonnull;
 
 import com.google.common.base.Preconditions;
+import com.google.errorprone.annotations.Immutable;
 
 /**
  * 表示年份与季度
- * 
+ *
  * @author zhouxy
  */
+@Immutable
 public final class YearQuarter implements Comparable<YearQuarter>, Serializable {
     private static final long serialVersionUID = 3804145964419489753L;
 
@@ -57,7 +59,7 @@ public final class YearQuarter implements Comparable<YearQuarter>, Serializable
 
     /**
      * 根据指定年份与季度，创建 {@link YearQuarter} 实例
-     * 
+     *
      * @param year 年份
      * @param quarter 季度
      * @return {@link YearQuarter} 实例
@@ -68,7 +70,7 @@ public final class YearQuarter implements Comparable<YearQuarter>, Serializable
 
     /**
      * 根据指定年份与季度，创建 {@link YearQuarter} 实例
-     * 
+     *
      * @param year 年份
      * @param quarter 季度
      * @return {@link YearQuarter} 实例
@@ -79,7 +81,7 @@ public final class YearQuarter implements Comparable<YearQuarter>, Serializable
 
     /**
      * 根据指定日期，判断日期所在的年份与季度，创建 {@link YearQuarter} 实例
-     * 
+     *
      * @param date 日期
      * @return {@link YearQuarter} 实例
      */
@@ -89,7 +91,7 @@ public final class YearQuarter implements Comparable<YearQuarter>, Serializable
 
     /**
      * 根据指定日期，判断日期所在的年份与季度，创建 {@link YearQuarter} 实例
-     * 
+     *
      * @param date 日期
      * @return {@link YearQuarter} 实例
      */
@@ -103,7 +105,7 @@ public final class YearQuarter implements Comparable<YearQuarter>, Serializable
 
     /**
      * 根据指定日期，判断日期所在的年份与季度，创建 {@link YearQuarter} 实例
-     * 
+     *
      * @param date 日期
      * @return {@link YearQuarter} 实例
      */
@@ -113,7 +115,7 @@ public final class YearQuarter implements Comparable<YearQuarter>, Serializable
 
     /**
      * 根据指定年月，判断其所在的年份与季度，创建 {@link YearQuarter} 实例
-     * 
+     *
      * @param yearMonth 年月
      * @return {@link YearQuarter} 实例
      */
@@ -238,7 +240,7 @@ public final class YearQuarter implements Comparable<YearQuarter>, Serializable
 
     /**
      * 返回 {@link YearQuarter} 的字符串表示形式，如 "2024 Q3"
-     * 
+     *
      * @return {@link YearQuarter} 的字符串表示形式
      */
     @Override