scala 交集 & 是如何实现的？匹配集合中的元素
我有两组对象，我想获得两组对象的交集。集合中的对象如下所示
@BeanInfo
class User {
@JsonProperty
@BeanProperty
var name:String = ""
@JsonProperty
@BeanProperty
var id:Long = 0
override def toString = name
override def equals(other: Any)= other match {
case other:User => other.id == this.id
case _ => false
}
}
在另一个类中，我获取用户集并希望查看交集。
val myFriends = friendService.getFriends("me")
val friendsFriends = friendService.getFriends("otheruser")
println(myFriends & friendsFriends)
上面的代码不起作用并打印
Set()
但是，如果我使用 foreach 手动循环集合，我会得到所需的结果
var matchedFriends:scala.collection.mutable.Set[User] = new HashSet[User]()
myFriends.foreach(myFriend => {
friendsFriends.foreach(myFriend => {
if(myFriend == myFriend){
matchedFriends.add(myFriend)
}
})
})
println(matchedFriends)
，上面的代码打印
Set(Matt, Cass, Joe, Erin)
工作得很好
val set1 = Set(1, 2, 3, 4)
val set2 = Set(4,5,6,7,1)
println(set1 & set2)
这
Set(1, 4)
。 &- 等..仅适用于原始对象？ 我是否必须对我的用户对象做一些额外的事情才能使其工作？
I have two sets of objets and I want to get the intersection of the two sets. The objects in the sets look like this
@BeanInfo
class User {
@JsonProperty
@BeanProperty
var name:String = ""
@JsonProperty
@BeanProperty
var id:Long = 0
override def toString = name
override def equals(other: Any)= other match {
case other:User => other.id == this.id
case _ => false
}
}
In another class I get the sets of users and want to see the intersection.
val myFriends = friendService.getFriends("me")
val friendsFriends = friendService.getFriends("otheruser")
println(myFriends & friendsFriends)
The above code does not work and prints
Set()
However if I manually loop over the sets using foreach I get the desired result
var matchedFriends:scala.collection.mutable.Set[User] = new HashSet[User]()
myFriends.foreach(myFriend => {
friendsFriends.foreach(myFriend => {
if(myFriend == myFriend){
matchedFriends.add(myFriend)
}
})
})
println(matchedFriends)
the above code prints
Set(Matt, Cass, Joe, Erin)
This works just fine
val set1 = Set(1, 2, 3, 4)
val set2 = Set(4,5,6,7,1)
println(set1 & set2)
The above prints
Set(1, 4)
Do the set operations & &- etc.. only work on primitive objects ?
Do I have to do something additional to my user object for this to work ?
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评论（3）
我对此并不是 100% 肯定，但我认为您的问题是由于实现了自定义
equals而没有相应的自定义hashCode引起的。实际上，我有点惊讶你的哈希集竟然能正常工作......当然，你对每个集合的元素的手动循环工作得很好，因为你根本不调用
hashCode： ）I'm not 100% positive about this, but I think your issue is caused by having implemented a custom
equalswithout a corresponding customhashCode. I'm sort of surprised your hash sets are working at all, actually...Your manual loop through the elements of each set works fine, of course, because you don't call
hashCodeat all :)来自 JavaDoc：
来自 ScalaDoc：
Set不起作用，因为您在覆盖equals时破坏了hashCode。From JavaDoc:
From ScalaDoc:
Setis not working because you brokehashCodewhen you overrodeequals.当重写
equals时，总是用它重写hashCode。When overriding
equalsalways overridehashCodewith it.