hashset

问题 How do I check if an array exists in a HashSet ? For example: int[] a = new int[]{0, 0}; HashSet<int[]> set = new HashSet<>(); set.add(a); Then: int[] b = new int[]{0, 0}; set.contains(b); // ===> true 回答1: Using arrays int[] a = new int[] { 0, 0 }; HashSet<int[]> set = new HashSet<>(); set.add(a); int[] b = new int[] { 0, 0 }; boolean contains = set.stream().anyMatch(c -> Arrays.equals(c, b)); System.out.println("Contains? " + contains); Output: Contains? true It doesn’t exploit the fast

问题 I already know that we use HashMap when we have Key-Value pair and we use HashSet when we do not need repetitive data. But I always get confused where Hashtable comes into play. Is it a totally different data structure? Or both HashMap and HashSet use hash function to store data in Hashtable ? Thorough explanation will be really helpful . 回答1: More specific, HashSet uses internally a HashMap , look at the implementation of HashSet.java private transient HashMap<E,Object> map; As stated in a

问题 is there any way I can declare constructor to take HashSet as one of arguments and then pass HashSet value directly as argument during object initialization? I mean something like this: public class Order { private Set<Product> products = new HashSet<Product>(); public Order (???) { this.products = ??? } } and then, while initializing object: Order order = new Order("product1", "product2", "product3"); is it possible? 回答1: You can use varargs : public class Order { private Set<Product>

问题 is there any way I can declare constructor to take HashSet as one of arguments and then pass HashSet value directly as argument during object initialization? I mean something like this: public class Order { private Set<Product> products = new HashSet<Product>(); public Order (???) { this.products = ??? } } and then, while initializing object: Order order = new Order("product1", "product2", "product3"); is it possible? 回答1: You can use varargs : public class Order { private Set<Product>

问题 I have 2 loops(nested), trying to do a simple parallelisation pseudocode : for item1 in data1 (~100 million row) for item2 in data2 (~100 rows) result = process(item1,item2) // couple of if conditions hashset.add(result) // while adding, incase of a duplicate i also decide wihch one to retain process(item1,item2) to be precise has 4 if conditions bases on values in item1 and item2.(time taken is less than 50ms) data1 size is Nx17 data2 size is Nx17 result size is 1x17 (result is joined into a

问题 I have a list that stores well over a million objects within it. I need to look through the list and update the objects found through the below query as efficiently as possible. I was thinking of using a Dictionary or HashSet, but I'm relatively new to C# and could not figure out how to implement these other two approaches. My current code is simply a LINQ statement searching through an IList. public IList<LandObject> landObjects = new List<LandObject>(); var lObjsToUpdate = from obj in

问题 I've been reading up on the differences between a HashMap , HashSet , and HashTable . A key thing I've been noticing is that I've seen that HashMap / HashSet are not synchronized while a HashTable is. However in a code base that I've seen before there are several places where a block like this is used: synchronized (hashSet) { //Some code involving the hashset } How is this possible if a HashSet isn't synchronized? Does the synchronized block simply allow us to use a non synchronous data

问题 I am wondering if it is possible to use a HashSet and make the method Contains to return true if one of the field is in the hash for a giving object. This is an example of what I would like static void Main(string[] args) { HashSet<Product> hash = new HashSet<Product>(); // Since the Id is the same, both products are considered to be the same even if the URI is not the same // The opposite is also true. If the URI is the same, both products are considered to be the same even if the Id is not

问题 I am wondering if it is possible to use a HashSet and make the method Contains to return true if one of the field is in the hash for a giving object. This is an example of what I would like static void Main(string[] args) { HashSet<Product> hash = new HashSet<Product>(); // Since the Id is the same, both products are considered to be the same even if the URI is not the same // The opposite is also true. If the URI is the same, both products are considered to be the same even if the Id is not

来源： https://stackoverflow.com/questions/15091937/list-throws-concurrentmodificationexception-but-set-does-not-throws-concurrentmo