目前Money还不够完善，比如没有考虑到值为负数的情况，这种情况应该是不存在的。下面重构Money类

    1. package com.lugew.springbootddd.snackmachine;
    3. import com.lugew.springbootddd.ValueObject;
    5. /**
    6.  * @author 夏露桂
    7.  * @since 2021/6/7 11:59
    8.  */
    10. public class Money extends ValueObject<Money> {
    11.     private final int oneCentCount;
    12.     private final int tenCentCount;
    13.     private final int quarterCount;
    14.     private final int oneDollarCount;
    15.     private final int fiveDollarCount;
    16.     private final int twentyDollarCount;
    18.     public Money(int oneCentCount, int tenCentCount, int quarterCount, int
    19.             oneDollarCount, int fiveDollarCount, int twentyDollarCount) {
    20.         if (oneCentCount < 0)
    21.             throw new IllegalStateException();
    22.         if (tenCentCount < 0)
    23.             throw new IllegalStateException();
    24.         if (quarterCount < 0)
    25.             throw new IllegalStateException();
    26.         if (oneDollarCount < 0)
    27.             throw new IllegalStateException();
    28.         if (fiveDollarCount < 0)
    29.             throw new IllegalStateException();
    30.         if (twentyDollarCount < 0)
    31.             throw new IllegalStateException();
    33.         this.oneCentCount = oneCentCount;
    34.         this.tenCentCount = tenCentCount;
    35.         this.quarterCount = quarterCount;
    36.         this.oneDollarCount = oneDollarCount;
    37.         this.fiveDollarCount = fiveDollarCount;
    38.         this.twentyDollarCount = twentyDollarCount;
    39.     }
    41.     public static Money add(Money money1, Money money2) {
    43.         return new Money(
    44.                 money1.oneCentCount + money2.oneCentCount,
    45.                 money1.tenCentCount + money2.tenCentCount,
    46.                 money1.quarterCount + money2.quarterCount,
    47.                 money1.oneDollarCount + money2.oneDollarCount,
    48.                 money1.fiveDollarCount + money2.fiveDollarCount,
    49.                 money1.twentyDollarCount + money2.twentyDollarCount);
    50.     }
    52.     @Override
    53.     protected boolean equalsCore(Money other) {
    54.         return oneCentCount == other.oneCentCount
    55.                 && tenCentCount == other.tenCentCount
    56.                 && quarterCount == other.quarterCount
    57.                 && oneDollarCount == other.oneDollarCount
    58.                 && fiveDollarCount == other.fiveDollarCount
    59.                 && twentyDollarCount == other.twentyDollarCount;
    60.     }
    62.     @Override
    63.     protected int getHashCodeCore() {
    64.         int hashCode = oneCentCount;
    65.         hashCode = (hashCode * 397) ^ tenCentCount;
    66.         hashCode = (hashCode * 397) ^ quarterCount;
    67.         hashCode = (hashCode * 397) ^ oneDollarCount;
    68.         hashCode = (hashCode * 397) ^ fiveDollarCount;
    69.         hashCode = (hashCode * 397) ^ twentyDollarCount;
    70.         return hashCode;
    71.     }
    72. }

    👆任何字段的值为零得话，程序会抛出IllegalStateException()异常。