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);
}
问题出在这一行:this.weeklyStats.put(date.toString(fmt), dailyIceCreamStock);
如您所见,我将随机生成的值添加到类型的 HashMap 中:
Map<String, List<IceCream>> weeklyStats
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]
期望的输出是在每个列表中都有随机值。 我猜,范围有问题,我不明白
最佳答案
您正在将同一个 List 实例多次添加到 Map。您应该创建列表的副本,以便在您的 map 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);
}
编辑:
实际上,这还不够,您还应该创建 IceCream 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);
}
关于java - HashMap 中每个键的值相同,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/31112396/