Java equivalent of c++ equal_range (or lower_bound & upper_bound)
binary-search, java, lower-bound, upperbound
Solution
In Java, you use `Collections.binarySearch` to find the lower bound of the equal range in a sorted list (`Arrays.binarySearch` provides a similar capability for arrays). This gives you a position within the equal range with no further guarantees:
If the list contains multiple elements equal to the specified object, there is no guarantee which one will be found.
Then you iterate linearly forward and then backward until you hit the end of the equal range.
These methods work for objects implementing the `Comparable` interface. For classes that do not implement the `Comparable`, you can supply an instance of a custom `Comparator` for comparing the elements of your specific type.
Problem
I have a List of object sorted and I want to find the first occurrence and the last occurrence of an object. In C++, I can easily use std::equal_range (or just one lower_bound and one upper_bound). For example: ``` bool mygreater (int i,int j) { return (i>j); } int main () { int myints[] = {10,20,30,30,20,10,10,20}; std::vector<int> v(myints,myints+8); // 10 20 30 30 20 10 10 20 std::pair<std::vector<int>::iterator,std::vector<int>::iterator> bounds; // using default comparison: std::sort (v.begin(), v.end()); // 10 10 10 20 20 20 30 30 bounds=std::equal_range (v.begin(), v.end(), 20); // ^ ^ // using "mygreater" as comp: std::sort (v.begin(), v.end(), mygreater); // 30 30 20 20 20 10 10 10 bounds=std::equal_range (v.begin(), v.end(), 20, mygreater); // ^ ^ std::cout << "bounds at positions " << (bounds.first - v.begin()); std::cout << " and " << (bounds.second - v.begin()) << '\n'; return 0; } ``` In Java, there seems to be no simple equivalence? How should I do with the equal range with ``` List<MyClass> myList; ``` By the way, I am using a standard import java.util.List;