Java Guava笛卡尔积 [英] Java Guava CartesianProduct
问题描述
我正在通过编写小的代码片段来探索Java Guava库.这是我为找到 笛卡尔积 个n个集合. 此处的文档
I am exploring Java Guava Library by writing small snippets of code. Here is what I wrote for finding the cartesian product of n-sets. Documentation here
//allLists populated above
...
List<Set> interimList = new ArrayList<Set>();
for(List<String> tmp : allLists) //converting List<List> to List<Set>
{
Set interimSet = new HashSet(tmp);
interimList.add(interimSet);
}
System.out.println(interimList);
Sets.cartesianProduct(interimList);
但是这没有编译.最后一行Sets.cartesianProduct
不接受List<Set>
.但是根据文档,这不是它的签名吗?
But this is not compiling. The last line Sets.cartesianProduct
is not accepting List<Set>
. But according to documentation isn't that its signature?
public static <B> Set<List<B>> cartesianProduct(List<? extends Set<? extends B>> sets)
错误消息: Cannot Resolve method cartesianProduct(java.util.List<java.util.Set)
推荐答案
问题是您创建的是原始的Set
,而不是通用的.
The problem is you have created a raw Set
, instead of a generic one.
会发生什么情况,您正在尝试将List<Set<Object extends String>>
传递给Sets.cartesianProduct()
,这就是为什么您收到编译类型错误的原因.
What happens is you're trying to pass a List<Set<Object extends String>>
to the Sets.cartesianProduct()
and this is why you're receiving a compile-type error.
它将编译:
List<Set<String>> interimList = new ArrayList<Set<String>>();
//converting List<List<String>> to List<Set<String>>
for (List<String> tmp : allLists) {
Set<String> interimSet = new HashSet<String>(tmp);
interimList.add(interimSet);
}
System.out.println(interimList);
Sets.cartesianProduct(interimList);
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