Java hashmap中每个键的值相同

我将从我的代码开始

 public void simulateSale(List<IceCream> dailyIceCreamStock) {
    date = LocalDate.now().minusDays(6);
    DateTimeFormatter fmt = DateTimeFormat.forPattern("yyyy-MM-dd");

    for (int i = 0; i < timeInterval; i++) {
        for(IceCream iceCream: dailyIceCreamStock){
            iceCream.setSoldCount(rand.nextInt(IceCream.AMOUNT + 1));
            iceCream.setStockDate(date);
        }

        //Every day should have different ArrayList of values
        this.weeklyStats.put(date.toString(fmt), dailyIceCreamStock);
        date = date.plusDays(1);
    }

问题是，当我迭代这个hashmap时，每个键都有相同的值列表。输出如下所示：

[11, 3, 11, 12, 20]
[11, 3, 11, 12, 20]
[11, 3, 11, 12, 20]
[11, 3, 11, 12, 20]
[11, 3, 11, 12, 20]
[11, 3, 11, 12, 20]
[11, 3, 11, 12, 20]

期望的输出是在该列表中的每一个中都有随机值。

---

我想，作用域存在一些问题，我不理解您多次将同一列表实例添加到映射中。您应该创建列表的副本，以便在地图中具有不同的值：

for (int i = 0; i < timeInterval; i++) {
    List<IceCream> copy = new ArrayList<>(dailyIceCreamStock); // create a copy
    for(IceCream iceCream: copy){ // modify the elements of the copy
        iceCream.setSoldCount(rand.nextInt(IceCream.AMOUNT + 1));
        iceCream.setStockDate(date);
    }

    //Every day should have different ArrayList of values
    this.weeklyStats.put(date.toString(fmt), copy); // put the copy in the Map
    date = date.plusDays(1);
}

for（int i=0；i

编辑：

实际上，这还不够，还应该创建冰淇淋实例的副本。否则，所有列表都将是不同的实例，但仍将包含相同的IceCream对象

for (int i = 0; i < timeInterval; i++) {
    List<IceCream> copy = new ArrayList<>();
    for(IceCream iceCream: dailyIceCreamStock){ 
        IceCream newIC = new IceCream(); // not sure if you want to copy any
                                         // data from the original IceCream
        newIC.setSoldCount(rand.nextInt(IceCream.AMOUNT + 1));
        newIC.setStockDate(date);
        copy.add(newIC); // add a new IceCream instance to the new List
    }

    //Every day should have different ArrayList of values
    this.weeklyStats.put(date.toString(fmt), copy); 
    date = date.plusDays(1);
}

for（int i=0；i

每次迭代，您都会修改相同的

列表dailyIceCreamStock

，因此

映射中的所有键都指向相同的列表

您可能希望在每次迭代时初始化并引用
列表的一个新的深度副本，并在执行随机突变后将其放入
映射中
 循环中没有变量。什么是timeInterval？timeInterval是全局int变量，在这种情况下，它的值是7，其他人回答时，dailyIceCreamStock对于每个周都是一样的。
for (int i = 0; i < timeInterval; i++) {
    List<IceCream> copy = new ArrayList<>();
    for(IceCream iceCream: dailyIceCreamStock){ 
        IceCream newIC = new IceCream(); // not sure if you want to copy any
                                         // data from the original IceCream
        newIC.setSoldCount(rand.nextInt(IceCream.AMOUNT + 1));
        newIC.setStockDate(date);
        copy.add(newIC); // add a new IceCream instance to the new List
    }

    //Every day should have different ArrayList of values
    this.weeklyStats.put(date.toString(fmt), copy); 
    date = date.plusDays(1);
}