comparator

问题 Why does the declaration look like this: default <U extends Comparable<? super U>> Comparator<T> thenComparing( Function<? super T, ? extends U> keyExtractor) I understand most of it. It makes sense that U can be anything as long as it's comparable to a superclass of itself, and thus also comparable to itself. But I don't get this part: Function<? super T, ? extends U> Why not just have: Function<? super T, U> Can't the U just parameterize to whatever the keyExtractor returns, and still

问题 Why does the declaration look like this: default <U extends Comparable<? super U>> Comparator<T> thenComparing( Function<? super T, ? extends U> keyExtractor) I understand most of it. It makes sense that U can be anything as long as it's comparable to a superclass of itself, and thus also comparable to itself. But I don't get this part: Function<? super T, ? extends U> Why not just have: Function<? super T, U> Can't the U just parameterize to whatever the keyExtractor returns, and still

问题 Need to sort class Dir by 3 String fields. First one: sort by 1 value - s1 ; Then sort by String length - s1+s2+s3 ; After sort by 2 value - s2 ; And sort by 3 value - s3 . In my code its works for value 1 and String length sorting, but sorting by 2 value does not works. How i can sorting class Dir by multiple values? Class Dir: public class Dir { private String s1 = ""; private String s2 = ""; private String s3 = ""; public Dir(String s1){ this.s1 = s1; } public Dir(String s1, String s2){

问题 This question already has answers here : How do I sort a vector of pairs based on the second element of the pair? (7 answers) Closed 6 years ago . vector<pair<int,int> > v; for(i=0;i<5;i++){ cin>>b>>c; v.push_back(make_pair(b,c)); } sort(v.begin(),v.end()); Is it possible to write a comparator for the sort function such that v[i].first is sorted in increasing order and for similar values of v[i].first , v[i].second is sorted in decreasing order? like:- i/p: 13 10 44 15 13 15 13 99 6 45 o/p: 6

问题 This question already has answers here : How do I sort a vector of pairs based on the second element of the pair? (7 answers) Closed 6 years ago . vector<pair<int,int> > v; for(i=0;i<5;i++){ cin>>b>>c; v.push_back(make_pair(b,c)); } sort(v.begin(),v.end()); Is it possible to write a comparator for the sort function such that v[i].first is sorted in increasing order and for similar values of v[i].first , v[i].second is sorted in decreasing order? like:- i/p: 13 10 44 15 13 15 13 99 6 45 o/p: 6

问题 I'm trying to sort a list with the following rules: Known values should be ordered before unknown values. Known values should be ordered by a separately defined key. Unknown values should be ordered by their natural ordering. I've got (1) and (2), just struggling with adding (3) in to the mix. So far I have this: List<String> values = Arrays.asList( "red", "orange", "yellow", "green", "blue", "indigo", "violet"); ImmutableMap<String, Integer> map = ImmutableMap.of("red", 1, "green", 2, "blue"

问题 I have a list of strings def123, abc999, zzz000, abc123, zzz111 . I want the list sorted such that first three characters are sorted in ascendng order and next three in descending. So the output should be abc999, abc123, def123, zzz111,zzz000 Is this possible? 回答1: Other answers have suggested you implement Comparator . That's no longer necessary with recent utility methods added to the interface in Java 8: list.sort(Comparator .comparing(s -> s.substring(0, 3)) .thenComparing(s -> s.subtring

问题 How exactly do you chain method references for instances with Java 8? Example: Collections.sort(civs,Comparator.comparing(Civilization::getStrategy.getStrategLevel)); getStrategy of a Civilization instance returns a Strategy object instance which has the instance method getStrategyLevel . Why doesn't the Comparator.comparing method return a comparator with it's functional interface implemented by the lambda expression? 回答1: In that case, you should use a lambda, you can't apply a method

问题 I am interested in using a generic Java class which can handle String or Integer data type. I'd like to utilize the comparison operator, but it appears to have a compile error: Operator < cannot be used on generic T How can I achieve using comparison operators such as <, >, =, etc. for T ? (Assuming T is Number or String ). public class Node<T> { public T value; public Node(){ } public void testCompare(T anotherValue) { if(value == anotherValue) System.out.println("equal"); else if(value <

问题 I was trying to make a map sort by value using a custom comparator but I couldn't figure out why I kept getting the error of "no matching call to compareByVal" Here's what I had in my main.cpp: #include <map> #include <iostream> struct compareByVal { bool operator[](const std::pair<int,int> & a, const std::pair<int,int> & b) return a.second < b.second; } int main() { std::map<int,int,compareByVal> hash; hash[1] = 5; hash[2] = 2; hash[3] = 10; std::cout << hash.begin()->first << std::endl; }