hashmap

问题 If you look at java's hashCode method inside hashMap, you will find: public int hashCode() { int h = 0; Iterator<Entry<K,V>> i = entrySet().iterator(); while (i.hasNext()) h += i.next().hashCode(); return h; } So when you insert things into hashMap, hashMap's hashCode will change. Thus, if we insert an empty hashMap into hashSet, then insert something to this hashMap, then call hashSet.contains(hashMap) , it will return false . Why does Java allow such behavior? This will easily cause

问题 If you look at java's hashCode method inside hashMap, you will find: public int hashCode() { int h = 0; Iterator<Entry<K,V>> i = entrySet().iterator(); while (i.hasNext()) h += i.next().hashCode(); return h; } So when you insert things into hashMap, hashMap's hashCode will change. Thus, if we insert an empty hashMap into hashSet, then insert something to this hashMap, then call hashSet.contains(hashMap) , it will return false . Why does Java allow such behavior? This will easily cause

问题 I'm attempting to define a method putIfGreaterThan() for my new Map class ( given a key it replaces the old value with the new value only if the new value is greater than the old value ). I understand I could accomplish this either via composition (by having a private final Map<String, Double> map; in new class and then passing a Map to constructor) or by implementing the Map interface in my new class and passing a Map to the constructor (although I'm not sure which approach is superior). My

问题 This question already has answers here : Printing HashMap In Java (15 answers) Closed 5 years ago . I'm trying to learn how hashmaps work and I've been fiddling with a small phonebook program. But I'm stumped at what to do when I want to print out all the keys. here's my code: import java.util.HashMap; import java.util.*; public class MapTester { private HashMap<String, String> phoneBook; public MapTester(){ phoneBook = new HashMap<String, String>(); } public void enterNumber(String name,

问题 Currently I am doing this: badLinks = Array.new badLinksFile = File.new(arrayFilePath + 'badLinks.txt', 'w+') badLinksFile.puts badLinks.to_json The array badLinks contains the hashes and is: brokenLink = Hash.new brokenLink[:onPage] = @lastPage brokenLink[:link] = @nextPage badLinks.push(brokenLink) When I look at the file it is empty. Should this work? 回答1: A couple things to check: badLinksFile = File.new(arrayFilePath + 'badLinks.txt', 'w+') should probably be 'w' instead of ' w+ '. From

问题 I'm looking for explanation why those two data structures are not equal: $ perl6 -e 'use Test; is-deeply [ { a => "b" } ], [ { a => "b" }, ];' not ok 1 - # Failed test at -e line 1 # expected: $[{:a("b")},] # got: $[:a("b")] Trailing comma in Hashes and Arrays is meaningless just like in P5: $ perl6 -e '[ 1 ].elems.say; [ 1, ].elems.say' 1 1 But without it Hash is somehow lost and it gets flattened to array of Pairs: $ perl6 -e '[ { a => "b", c => "d" } ].elems.say;' 2 I suspect some Great

问题 In the HashMap documentation, it is mentioned that: the initial capacity is simply the capacity at the time the hash table is created the capacity is the number of buckets in the hash table. Now suppose we have intial capacity of 16 (default), and if we keep adding elements to 100 nos, the capacity of hashmap is 100 * loadfactor. Will the number of hash buckets is 100 or 16? Edit: From the solution I read: buckets are more than the elements added. Taking this as view point: so if we add

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 This question already has answers here : How to create a HashMap with two keys (Key-Pair, Value)? (12 answers) Closed 3 years ago . Can I have a hash map in Java that looks like this? HashMap<String, String, Integer> hmap = new HashMap<String, String, Integer>() My question is similar to this one hereQuestion I'm a newbie to Java. So what I want to know is, what would be the best data structure to use if I need something like above, if that is not valid? 回答1: Create a simple class holding two

问题 I have JSON structure like this: { "person": { "name": "snoop", "age": "22", "sex": "male" } } And beans like this: public class Person { HashMap<String,String> map; //getters and setters } I want all key and value from JSON to be filled inside map from Person class. I do not want to create bean for each key from JSON like int age , String name etc. I have tried following example and it worked for normal JSON structure like below: { "type": "Extends", "target": "application", "ret": "true" }