添加计算方法。

src/main/java/xyz/zhouxy/plusone/commons/time/Quarter.java

@@ -5,6 +5,7 @@ import java.time.MonthDay;
 
 import com.google.common.base.Preconditions;
 
+import xyz.zhouxy.plusone.commons.annotation.StaticFactoryMethod;
 import xyz.zhouxy.plusone.commons.util.Numbers;
 
 /**
@@ -45,6 +46,8 @@ public enum Quarter {
         this.firstMonth = this.lastMonth - 2;
     }
 
+    // StaticFactoryMethods
+
     /**
      * 根据给定的月份值返回对应的季度
      * 
@@ -52,6 +55,7 @@ public enum Quarter {
      * @return 对应的季度
      * @throws IllegalArgumentException 如果月份值不在有效范围内（1到12），将抛出异常
      */
+    @StaticFactoryMethod(Quarter.class)
     public static Quarter fromMonth(int monthValue) {
         Preconditions.checkArgument(Numbers.between(monthValue, 1, 13), "Invalid value for MonthOfYear: " + monthValue);
         return of(computeQuarterValueInternal(monthValue));
@@ -63,6 +67,7 @@ public enum Quarter {
      * @param month 月份
      * @return 对应的季度
      */
+    @StaticFactoryMethod(Quarter.class)
     public static Quarter fromMonth(Month month) {
         final int monthValue = month.getValue();
         return of(computeQuarterValueInternal(monthValue));
@@ -86,6 +91,7 @@ public enum Quarter {
      * @return 对应的季度
      * @throws IllegalArgumentException 如果季度值不在有效范围内（1到4），将抛出异常
      */
+    @StaticFactoryMethod(Quarter.class)
     public static Quarter of(int value) {
         if (value < 1 || value > 4) {
             throw new IllegalArgumentException("Invalid value for Quarter: " + value);
@@ -93,6 +99,21 @@ public enum Quarter {
         return ENUMS[value - 1];
     }
 
+    // StaticFactoryMethods end
+
+    // computs
+
+    public Quarter plus(long quarters) { // TODO 单元测试
+        final int amount = (int) ((quarters % 4) + 4);
+        return ENUMS[(ordinal() + amount) % 4];
+    }
+
+    public Quarter minus(long quarters) { // TODO 单元测试
+        return plus(-(quarters % 4));
+    }
+
+    // computs end
+
     // Getters
 
     public int getValue() {

src/main/java/xyz/zhouxy/plusone/commons/time/YearQuarter.java

@@ -1,5 +1,7 @@
 package xyz.zhouxy.plusone.commons.time;
 
+import static java.time.temporal.ChronoField.YEAR;
+
 import java.io.Serializable;
 import java.time.LocalDate;
 import java.time.Month;
@@ -29,6 +31,14 @@ public final class YearQuarter implements Comparable<YearQuarter>, Serializable
     /** 季度结束日期 */
     private final LocalDate lastDate;
 
+    private YearQuarter(int year, int quarter) {
+        Preconditions.checkNotNull(quarter, "Quarter can not be null.");
+        this.year = year;
+        this.quarter = Quarter.of(quarter);
+        this.firstDate = this.quarter.firstMonthDay().atYear(year);
+        this.lastDate = this.quarter.lastMonthDay().atYear(year);
+    }
+
     private YearQuarter(int year, @Nonnull Quarter quarter) {
         Preconditions.checkNotNull(quarter, "Quarter can not be null.");
         this.year = year;
@@ -136,6 +146,37 @@ public final class YearQuarter implements Comparable<YearQuarter>, Serializable
 
     // Getters end
 
+    // computes
+
+    public YearQuarter plusQuarters(long quartersToAdd) { // TODO 单元测试
+        if (quartersToAdd == 0) {
+            return this;
+        }
+        long quarterCount = this.year * 4L + (this.quarter.getValue() - 1);
+        long calcQuarters = quarterCount + quartersToAdd; // safe overflow
+        int newYear = YEAR.checkValidIntValue(Math.floorDiv(calcQuarters, 4));
+        int newQuarter = (int) Math.floorMod(calcQuarters, 4) + 1;
+        return of(newYear, Quarter.of(newQuarter));
+    }
+
+    public YearQuarter minusQuarters(long quartersToAdd) { // TODO 单元测试
+        return plusQuarters(-quartersToAdd);
+    }
+
+    public YearQuarter plusYears(long yearsToAdd) { // TODO 单元测试
+        if (yearsToAdd == 0) {
+            return this;
+        }
+        int newYear = YEAR.checkValidIntValue(this.year + yearsToAdd);  // safe overflow
+        return of(newYear, this.quarter);
+    }
+
+    public YearQuarter minusYears(long yearsToAdd) {
+        return plusYears(-yearsToAdd);
+    }
+
+    // computes end
+
     // hashCode & equals
 
     @Override

src/test/java/xyz/zhouxy/plusone/commons/time/QuarterTests.java

@@ -203,7 +203,7 @@ class QuarterTests {
     @Test
     void testFirstDayOfYear() {
         int firstDayOfYear;
-        
+
         firstDayOfYear = Quarter.Q1.firstDayOfYear(true);
         assertEquals(1, firstDayOfYear);
         firstDayOfYear = Quarter.Q1.firstDayOfYear(false);