Money类还缺少几个方法：getAmount获取金额的简易表示方式；substract减法。但是，此时不建议实现这两个方法，因为没有任何类会使用，这种方式违背了YAGNI原则，非常不可取。我为了走捷径实现了这些方法：

    1. package com.lugew.springbootddd.snackmachine;
    3. import com.lugew.springbootddd.ValueObject;
    4. import lombok.Getter;
    6. /**
    7.  * @author 夏露桂
    8.  * @since 2021/6/7 11:59
    9.  */
    10. @Getter
    11. public class Money extends ValueObject<Money> {
    12.     private final int oneCentCount;
    13.     private final int tenCentCount;
    14.     private final int quarterCount;
    15.     private final int oneDollarCount;
    16.     private final int fiveDollarCount;
    17.     private final int twentyDollarCount;
    18.     private float amount;
    20.     public float getAmount() {
    21.         return oneCentCount * 0.01f + tenCentCount * 0.10f + quarterCount * 0.25f +
    22.                 oneDollarCount * 1f
    23.                 + fiveDollarCount * 5f + twentyDollarCount * 20f;
    24.     }
    26.     public Money(int oneCentCount, int tenCentCount, int quarterCount, int
    27.             oneDollarCount, int fiveDollarCount, int twentyDollarCount) {
    28.         if (oneCentCount < 0)
    29.             throw new IllegalStateException();
    30.         if (tenCentCount < 0)
    31.             throw new IllegalStateException();
    32.         if (quarterCount < 0)
    33.             throw new IllegalStateException();
    34.         if (oneDollarCount < 0)
    35.             throw new IllegalStateException();
    36.         if (fiveDollarCount < 0)
    37.             throw new IllegalStateException();
    38.         if (twentyDollarCount < 0)
    39.             throw new IllegalStateException();
    41.         this.oneCentCount = oneCentCount;
    42.         this.tenCentCount = tenCentCount;
    43.         this.quarterCount = quarterCount;
    44.         this.oneDollarCount = oneDollarCount;
    45.         this.fiveDollarCount = fiveDollarCount;
    46.         this.twentyDollarCount = twentyDollarCount;
    47.     }
    49.     public Money substract(Money other) {
    50.         return new Money(
    51.                 oneCentCount - other.oneCentCount,
    52.                 tenCentCount - other.tenCentCount,
    53.                 quarterCount - other.quarterCount,
    54.                 oneDollarCount - other.oneDollarCount,
    55.                 fiveDollarCount - other.fiveDollarCount,
    56.                 twentyDollarCount - other.twentyDollarCount);
    57.     }
    59.     public static Money add(Money money1, Money money2) {
    61.         return new Money(
    62.                 money1.oneCentCount + money2.oneCentCount,
    63.                 money1.tenCentCount + money2.tenCentCount,
    64.                 money1.quarterCount + money2.quarterCount,
    65.                 money1.oneDollarCount + money2.oneDollarCount,
    66.                 money1.fiveDollarCount + money2.fiveDollarCount,
    67.                 money1.twentyDollarCount + money2.twentyDollarCount);
    68.     }
    70.     @Override
    71.     protected boolean equalsCore(Money other) {
    72.         return oneCentCount == other.oneCentCount
    73.                 && tenCentCount == other.tenCentCount
    74.                 && quarterCount == other.quarterCount
    75.                 && oneDollarCount == other.oneDollarCount
    76.                 && fiveDollarCount == other.fiveDollarCount
    77.                 && twentyDollarCount == other.twentyDollarCount;
    78.     }
    80.     @Override
    81.     protected int getHashCodeCore() {
    82.         int hashCode = oneCentCount;
    83.         hashCode = (hashCode * 397) ^ tenCentCount;
    84.         hashCode = (hashCode * 397) ^ quarterCount;
    85.         hashCode = (hashCode * 397) ^ oneDollarCount;
    86.         hashCode = (hashCode * 397) ^ fiveDollarCount;
    87.         hashCode = (hashCode * 397) ^ twentyDollarCount;
    88.         return hashCode;
    89.     }
    90. }

    👆注意：只有Getter注解而没有Setter注解，这使我们保持了对象的封闭性。