我有以下类:如何获得Comparator.comparing正确推断类型参数?
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import org.apache.commons.lang3.tuple.Pair;
public class Sorter {
private List<Pair<Long, NameDTO>> dtoPairs = new ArrayList<>();
public Sorter() {
Comparator<Pair<Long, NameDTO>> bySize = Comparator.comparing(Pair::getLeft);
Comparator<Pair<Long, NameDTO>> byName = Comparator.comparing(p -> p.getRight().getName());
dtoPairs.sort(bySize.reversed().thenComparing(byName));
}
}
class NameDTO {
private String name;
public String getName() {
return name;
}
}
这将编译没有问题。但是,如果我尝试内联变量是这样的:
dtoPairs.sort(Comparator.comparing(Pair::getLeft).reversed().thenComparing(Comparator.comparing(p -> p.getRight().getName())));
我得到以下编译错误:
Sorter.java:[18,51] incompatible types: cannot infer type-variable(s) T,U
(argument mismatch; invalid method reference
method getLeft in class org.apache.commons.lang3.tuple.Pair<L,R> cannot be applied to given types
required: no arguments
found: java.lang.Object
reason: actual and formal argument lists differ in length)
我怎么能写这样的表达使Java正确理解的参数?
的[对比和thenComparing给出编译错误]可能的复制(http://stackoverflow.com/questions/40500280/comparing-and-thencomparing-gives-compile-error) –
@ OleV.V:我不知道认为这是重复的,它没有泛泛的方法参考,这是什么扔我在这里。 – Keppil