collections

问题 Is there a standard way to represent a "set" that can contain duplicate elements. As I understand it, a set has exactly one or zero of an element. I want functionality to have any number. I am currently using a dictionary with elements as keys, and quantity as values, but this seems wrong for many reasons. Motivation: I believe there are many applications for such a collection. For example, a survey of favourite colours could be represented by: survey = ['blue', 'red', 'blue', 'green'] Here,

问题 I have tried below code String s[]={"1","2","3","4"}; Collection c=Arrays.asList(s); System.out.println(c.remove("1") +" remove flag"); System.out.println(" collcetion "+c); I was getting Exception in thread "main" java.lang.UnsupportedOperationException at java.util.AbstractList.remove(Unknown Source) at java.util.AbstractList$Itr.remove(Unknown Source) at java.util.AbstractCollection.remove(Unknown Source) at test.main(test.java:26) Can anyone help me to solve this issue? 回答1: Easy work

问题 Ok so i am new to these HashMaps but have some idea about LinkedLists and HashMaps. It would be great if you could give me some simple explanation regarding LinkedHashMap and as in the titile does this mean we are explicitly defining it to be of some type? 回答1: A LinkedHashMap is a combination of hash table and linked list. It has a predictable iteration order (a la linked list), yet the retrieval speed is that of a HashMap. The order of the iteration is determined by the insertion order, so

问题 In Java , there is thread-safe version HashMap named ConcurrentHashMap and thread-safe version TreeMap named ConcurrentSkipListMap, but there is no ConcurrentHashSet for HashSet. Instead, there are usually 4 ways to use thread-safe Set : Set<String> mySet = Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>()); Set<String> s = Collections.synchronizedSet(new HashSet<String>()); ConcurrentSkipListSet<E> CopyOnWriteArraySet<E> 1 use keySet() of ConcurrentHashMap to achieve both

问题 If I have a method that requires a parameter that, Has a Count property Has an integer indexer (get-only) What should the type of this parameter be? I would choose IList<T> before .NET 4.5 since there was no other indexable collection interface for this and arrays implement it, which is a big plus. But .NET 4.5 introduces the new IReadOnlyList<T> interface and I want my method to support that, too. How can I write this method to support both IList<T> and IReadOnlyList<T> without violating the

问题 With a list you can do: list.AddRange(otherCollection); There is no add range method in a HashSet . What is the best way to add another collection to a HashSet? 回答1: For HashSet<T> , the name is UnionWith. This is to indicate the distinct way the HashSet works. You cannot safely Add a set of random elements to it like in Collections , some elements may naturally evaporate. I think that UnionWith takes its name after "merging with another HashSet ", however, there's an overload for IEnumerable

问题 Can someone please provide an example of creating a Java ArrayList and HashMap on the fly? So instead of doing an add() or put() , actually supplying the seed data for the array/hash at the class instantiation? To provide an example, something similar to PHP for instance: $array = array (3, 1, 2); $assoc_array = array( 'key' => 'value' ); 回答1: List<String> list = new ArrayList<String>() { { add("value1"); add("value2"); } }; Map<String,String> map = new HashMap<String,String>() { { put("key1"

问题 what is the difference among list, queue and set? 回答1: In brief: A list is an ordered list of objects, where the same object may well appear more than once. For example: [1, 7, 1, 3, 1, 1, 1, 5]. It makes sense to talk about the "third element" in a list. You can add an element anywhere in the list, change an element anywhere in the list, or remove an element from any position in the list. A queue is also ordered, but you'll only ever touch elements at one end. All elements get inserted at

问题 I use several maps and sets. The lack of contiguous memory, and high number of (de)allocations, is a performance bottleneck. I need a mainly STL-compatbile map and set class which can use a contiguous block of memory for internal objects (or multiple blocks). It also needs to have a reserve function so that I can preallocate for expected sizes. Before I write my own I'd like to check what is available first. Is there something in Boost which does this? Does somebody know of an available

问题 I'm trying to write a method which accepts any type of collection CC[_] and maps it to a new collection (the same collection type but a different element type) and I am struggling royally. Basically I'm trying to implement map but not on the collection itself . The Question I'm trying to implement a method with a signature which looks a bit like: def map[CC[_], T, U](cct: CC[T], f: T => U): CC[U] It's usage would be: map(List(1, 2, 3, 4), (_ : Int).toString) //would return List[String] I'm