hashset

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Efficiently finding the intersection of a variable number of sets of strings Say, have two Hashset, how to calculate the intersection of them? Set<String> s1 = new HashSet<String>(); Set<String> s2 = new HashSet<String>(); S1 INT S2 ? 回答1: Use the retainAll() method of Set: Set<String> s1; Set<String> s2; s1.retainAll(s2); // s1 now contains only elements in both sets If you want to preserve the sets, create a

问题 ===update==== from comment so I clearly read the doc and know it's not thread safe and I wanted to run a small experiment to see how it will break. So the doc says the result is non deterministic. Does anyone know what could happen? If I want to prove it's not thread safe how can I write a sample code so that I can actually see that it's no thread safe? Have you guys actually tried and seen not working example? Do you have sample code? If I have three threads accessing the hashset of string.

问题 For the below code it outputs " 1 ". and second code outputs " 2 " I don't understand why this is happening. Is it because I am adding the same object? How should I achieve the desired output 2. import java.util.*; public class maptest { public static void main(String[] args) { Set<Integer[]> set = new HashSet<Integer[]>(); Integer[] t = new Integer[2]; t[0] = t[1] = 1; set.add(t); Integer[] t1 = new Integer[2]; t[0] = t[1] = 0; set.add(t); System.out.println(set.size()); } } Second Code:

问题 I have a program for my Java class where I want to use hashSets to compare a directory of text documents. Essentially, my plan is to create a hashSet of strings for each paper, and then add two of the papers hashSets together into one hashSet and find the number of same 6-word sequences. My question is, do I have to manually check for, and handle, collisions, or does Java do that for me? 回答1: Java Hash Maps/Sets Automatically handel Hash collisions, this is why it is important to override

问题 I have a query regarding iterator of HashSet in Java. In book "Java Generics and Collections", following is stated: The chief attraction of a hash table implementation for sets is the (ideally) constanttime performance for the basic operations of add, remove, contains, and size. Its main disadvantage is its iteration performance; since iterating through the table involves examining every bucket, its cost is proportional to the table size regardless of the size of the set it contains. It

问题 This question already has answers here : Ordering of elements in Java HashSet (2 answers) Closed last year . When I run below code it is always giving the o/p in natural/ alphabetical order. As per I know HashSet doesn't sort the entries. I know that HashSet is backed by HashMap and not LinkedHashMap . I tried to explore the source code of HashSet and HashMap but couldn't find the code for this behavior. From the source code there is below constructor in HashSet class: HashSet(int

问题 Consider the following situation: public abstract class Vegetable {}; public class Tomato extends Vegetable {}; public class Cucumber extends Vegetable {}; public class Orange {}; The point is - I want my HashSet to store only something extending Vegetable , how do I do this? This should be simple.. ..but Set <? extends Vegetable> () hs = new HashSet <? extends Vegetable> (); is not a working construction of course, Java wants me to specify what type of Set I want - Tomato or Cucumber , what

问题 This question already has answers here : Convert an array to a HashSet<T> in .NET (7 answers) Closed 4 years ago . I have a List that has duplicates of objects. To solve that, I need to convert the List into a HashSet (in C#). Does anyone know how? 回答1: Make sure your object's class overrides Equals and GetHashCode and then you can pass the List<T> to HashSet<T> constructor. var hashSet = new HashSet<YourType>(yourList); You may see: What is the best algorithm for an overridden System.Object

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Maximum Size of HashSet How can I add distinct ip address in HashSet Set<String> ips = new HashSet<String>(); String ip = generateIPAddress(); if (!ips.add(ip)) { // What should I do here? } private String generateIPAddress() { Random r = new Random(); //Now the IP is b1.b2.b3.b4 String s = r.nextInt(256) + "." + r.nextInt(256) + "." + r.nextInt(256) + "." + r.nextInt(256); return s; } 回答1: add() returns true if

问题 i have a class where i am inserting data into a array-list based on the id provided. I am passing a bookId into my class and by comparing bookid i am get a book object. And after getting that object(book) ,am inserting into my arraylist. Now I do't want to insert same data more then once. If a same bookid passes in the class then only it should store once. i am storing my arraylist into session. please check my code. And suggest me a solution for my problem. How to avoid duplicate insertion