collections

问题 what would be the opposite of intersect in groovy collections? 回答1: You probably want to combine both the answers from @Andre and @denis I think what you want is the union and then subtract the intersection from this def a = [1,2,3,4,5] def b = [2,3,4] assert [1,5] == ( a + b ) - a.intersect( b ) The solution given by denis would depend on whether you do def opposite = leftCollection-rightCollection // [1,5] or def opposite = rightCollection-leftCollection // [] which I don't think you wanted

问题 I have a conundrum that's caused me to ponder whether there are any standard java classes that implement Iterable<T> without also implementing Collection<T> . I'm implementing one interface that requires me to define a method that accepts an Iterable<T> , but the object I'm using to back this method requires a Collection<T> . This has me doing some really kludgy feeling code that give some unchecked warnings when compiled. public ImmutableMap<Integer, Optional<Site>> loadAll( Iterable<?

问题 I been working on a problem for hours now and it seems I can not find a way to get the above sorting to work. In an magento project (im relatively new to magento) I have to sort the collection first by subcategory, then an attribute and last by the product name. is Anchor is set to ture with all categories, so parent categories also show subcategory products. I came across an idea of using the ReflectionObject using the usort() PHP function with an comparator function, like this: private

问题 I been working on a problem for hours now and it seems I can not find a way to get the above sorting to work. In an magento project (im relatively new to magento) I have to sort the collection first by subcategory, then an attribute and last by the product name. is Anchor is set to ture with all categories, so parent categories also show subcategory products. I came across an idea of using the ReflectionObject using the usort() PHP function with an comparator function, like this: private

问题 I am trying to sort based on a function. I am currently doing the following, and it works. var _criteria = ... some search criteria var _pageNumber = ... the page num I want to see var _nPerPage = ... the number of documents per page var _sort = {}; _sort.name = ... the column name I am sorting on _sort.order = ... asc or desc sort Collection.find(_criteria) .skip((_pageNumber-1)*_nPerPage) .limit(_nPerPage) .sort(_sort.name,_sort.order) .execFind(function (err, docs) { ... }); Now I would

问题 I am trying to sort based on a function. I am currently doing the following, and it works. var _criteria = ... some search criteria var _pageNumber = ... the page num I want to see var _nPerPage = ... the number of documents per page var _sort = {}; _sort.name = ... the column name I am sorting on _sort.order = ... asc or desc sort Collection.find(_criteria) .skip((_pageNumber-1)*_nPerPage) .limit(_nPerPage) .sort(_sort.name,_sort.order) .execFind(function (err, docs) { ... }); Now I would

问题 Java is throwing ConcurrentModificationException when I am running the following code. Any idea why is that? ArrayList<String> list1 = new ArrayList<String>(); list1.add("Hello"); list1.add("World"); list1.add("Good Evening"); for (String s : list1){ list1.remove(2); System.out.println(s); } 回答1: If you take a look at documentation of ConcurrentModificationException you will find that This exception may be thrown by methods that have detected concurrent modification of an object when such

问题 Wondering is there more simple way than computing the character count of a given string as below? String word = "AAABBB"; Map<String, Integer> charCount = new HashMap(); for(String charr: word.split("")){ Integer added = charCount.putIfAbsent(charr, 1); if(added != null) charCount.computeIfPresent(charr,(k,v) -> v+1); } System.out.println(charCount); 回答1: Simplest way to count occurrence of each character in a string, with full Unicode support (Java 11+) 1 : String word = "AAABBB"; Map<String

问题 I am not sure the defects of Immutable collections I understand is correct, so I list them in this answer. Hope someone corrects me here. a): Comparing to Collections.unmodifiableXXX(), ImmutableXXX.copyOf() loses the source collection feature . For example, when a linkedList is put into ImmutableList.copyOf(), the ImmutableList is not linked anymore. Same as Tree based collection. b): People think Collections.unmodifiableXXX just uses same reference of source collection, so once the source

问题 I need to do something like this... Collection<T> myCollection; ///assume it is initialized and filled for(Iterator<?> index = myCollection.iterator(); index.hasNext();) { Object item = index.next(); myCollection.remove(item); } Obviously this throws ConcurrentModificationException... So I have tried this but doesn't does seem elegant/efficient and throws a Type safety: Unchecked cast from Object to T warning Object[] list = myCollection.toArray(); for(int index = list.length - 1; index >= 0;