Your code takes an array of numbers and a target number/sum. It then returns the indexes in the array for two numbers which add up to the target number/sum. Consider an array of numbers such as [1, 2, 3] and a target of 5. Your task is to find the two numbers in this array … Read more
Sure, you can use PowerShell’s native CliXml format: @{ a = 1 b = [pscustomobject]@{ prop = “value” } } | Export-Clixml -Path hashtable.ps1xml Deserialize with Import-CliXml: PS C:\> $ht = Import-CliXml hashtable.ps1xml PS C:\> $ht[‘b’].prop -eq ‘value’ True
Presented with no comment beyond read all the other comments and answers to understand why you probably don’t want to do this: use std::{collections::HashMap, hash}; #[derive(Debug, Copy, Clone)] struct DontUseThisUnlessYouUnderstandTheDangers(f64); impl DontUseThisUnlessYouUnderstandTheDangers { fn key(&self) -> u64 { self.0.to_bits() } } impl hash::Hash for DontUseThisUnlessYouUnderstandTheDangers { fn hash<H>(&self, state: &mut H) where H: hash::Hasher, { … Read more
You are on the right track using ConcurrentHashMap. For each point: Check out the methods putIfAbsent and replace both are threadsafe and combine checking current state of hashmap and updating it into one atomic operation. The get method is not synchronized internally but will return the most recent value for the specified key available to … Read more
Hashtable is the older class, and its use is generally discouraged. Perhaps they saw the need for a null key, and more importantly – null values, and added it in the HashMap implementation. HashMap is newer, and has more advanced capabilities, which are basically just an improvement on the Hashtable functionality. When HashMap was created, … Read more
Since Java 8 you can make use of Map#computeIfAbsent(). Map<String, List<User>> usersByCountry = new HashMap<>(); for (User user : listOfUsers) { usersByCountry.computeIfAbsent(user.getCountry(), k -> new ArrayList<>()).add(user); } Or, make use of Stream API’s Collectors#groupingBy() to go from List to Map directly: Map<String, List<User>> usersByCountry = listOfUsers.stream().collect(Collectors.groupingBy(User::getCountry)); In Java 7 or below, best what you can … Read more
There are no aliases in Java. You can extend the HashMap class with your class like this: public class TheNewType extends HashMap<String, String> { // default constructor public TheNewType() { super(); } // you need to implement the other constructors if you need } But keep in mind that this will be a class it … Read more
If you need a map and keys in order, those are 2 different things, you need 2 different (data) types to provide that functionality. With a keys slice The easiest way to achieve this is to maintain key order in a different slice. Whenever you put a new pair into the map, first check if … Read more
This was fixed by changing my Eclipse IDE version from indigo to luna. Luna comes with support for Java 8 so all issues have now been resolved.
Actually, it’s not just HashSet. All implementations of the Set interface in Java 6 are based on an underlying Map. This is not a requirement; it’s just the way the implementation is. You can see for yourself by checking out the documentation for the various implementations of Set. Your main questions are But, why is … Read more