英文:
Grouping by ranges with Java 8 Stream API
问题
以下是您要求的翻译内容：
正如标题所示，我正在尝试使用 groupingBy 来根据它们的“能量级别”范围对对象列表进行分组。我对 Java Stream API 还非常陌生，所以我不太了解其中的操作方式。我编写的代码无法编译，我不确定原因是什么，我觉得我有正确的想法，但它没有起作用。任何帮助将不胜感激！您可以在下面找到我的尝试代码。
以下是我的 groupingBy 尝试：
Map<BigDecimal, List<Employee>> ranges = ObjectList.stream()
.collect(Collectors.groupingBy(a -> {
if(a.powerLevel < 2500) { a.powerLevel = LOWER;}
else if(a.powerLevel > 10000) {a.powerLevel = UPPER;}
else {a.powerLevel = MIDDLE;}
}
));
以下是我的枚举类：
enum salaryRanges {
LOWER, MIDDLE, UPPER
}
附注：我尝试过是否可以创建一个具有范围的枚举类，但根据我阅读的内容，在 Java 中这是不可能的。
英文:
As the title implies, I am trying to is groupingBy to group a list of objects by range of their "power levels". I am very new to Java Stream API, so I don't quite know my way around it. The code I have written won't compile and I'm just not certain why, I think I have the right idea, but it's not working. Any help would be greatly appreciated! You can find my failed attempt below.
This is the groupingBy attempt:
Map<BigDecimal, List<Employee>> ranges = ObjectList.stream()
.collect(Collectors.groupingBy(a -> {
if(a.powerLevel < 2500) { a.powerLevel = LOWER;}
else if(a.powerLevel >10000) {a.powerLevel = UPPER;}
else {a.PowerLevel = MIDDLE;}
}
));
This is my enum:
enum salaryRanges {
LOWER, MIDDLE, UPPER
}
PS:I tried to see if I could make an enum with ranges, but from what I've read that it not possible in Java.
答案1
得分: 2
我建议将逻辑移动到不同的方法中，用于定义范围
public static salaryRanges getRange(Employee employee) {
if(employee.powerLevel < 2500){
return salaryRanges.LOWER;
}
if(employee.powerLevel > 10000){
return salaryRanges.UPPER;
}
return salaryRanges.MIDDLE;
}
然后使用 Collectors.groupingBy
Map<salaryRanges,List<Employee>> res = list.stream()
.collect(Collectors.groupingBy(JavaMain::getRange));
您还可以像 @Andreas 建议的那样，通过将定义薪资范围逻辑移到枚举中来以另一种方式完成
enum salaryRanges {
LOWER, MIDDLE, UPPER
public static salaryRanges fromPowerLevel(int powerLevel){
if(powerLevel < 2500){
return salaryRanges.LOWER;
}
if(powerLevel > 10000){
return salaryRanges.UPPER;
}
return salaryRanges.MIDDLE;
}
}
然后使用 lambda 表达式调用该方法
Map<salaryRanges,List<Employee>> res = list.stream()
.collect(Collectors.groupingBy(emp -> salaryRanges.fromPowerLevel(emp.powerLevel)));
英文:
I would recommended to move logic into different method that defines range
public static salaryRanges getRange(Employee employee) {
if(employee.powerLevel < 2500){
return salaryRanges.LOWER;
}
if(employee.powerLevel > 10000){
return salaryRanges.UPPER;
}
return salaryRanges.MIDDLE;
}
Then use Collectors.groupingBy
Map<salaryRanges,List<Employee>> res = list.stream()
.collect(Collectors.groupingBy(JavaMain::getRange));
You can also do it in another way as @Andreas suggested, by moving defining salary range logic into enum
enum salaryRanges {
LOWER, MIDDLE, UPPER
public static salaryRanges fromPowerLevel(int powerLevel){
if(powerLevel<2500){
return salaryRanges.LOWER;
}
if(powerLevel>10000){
return salaryRanges.UPPER;
}
return salaryRanges.MIDDLE;
}
}
And then calling that method using lambda expression
Map<salaryRanges,List<Employee>> res = list.stream()
.collect(Collectors.groupingBy(emp->salaryRanges.fromPowerLevel(emp.powerLevel)));
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