>>> is the logical right shift (no sign-extension) (JLS 15.19 Shift Operators), and ^ is the bitwise exclusive-or (JLS 15.22.1 Integer Bitwise Operators). As to why this is done, the documentation offers a hint: HashMap uses power-of-two length tables, and hashes keys by masking away the higher bits and taking only the lower bits of … Read more
You can do it like you assumed. But your HashMap has to be templated: Map<String, Map<String, String>> map = new HashMap<String, Map<String, String>>(); Otherwise you have to do a cast to Map after you retrieve the second map from the first. Map map = new HashMap(); ((Map)map.get( “keyname” )).get( “nestedkeyname” );
require ‘json’ value=”{“key_1″:”value_1”, “key_2″:”value_2″}” puts JSON.parse(value) # => {“key_1″=>”value_1″,”key_2″=>”value_2”}
Though maps and slices in go are generic themselves, they are not covariant (nor could they be, since interfaces aren’t generics). It’s part of working with a language that doesn’t have generics, you will have to repeat some things. If you really just need to get the keys of any old map, you can use … Read more
The idea is that clear() is only called when you want to re-use the HashMap. Reusing an object should only be done for the same reason it was used before, so chances are that you’ll have roughly the same number of entries. To avoid useless shrinking and resizing of the Map the capacity is held … Read more
It seems like I could create a Hasher (e.g. RandomState), use that to manually calculate hash values, then store the u64 result in a HashMap<u64, _> but that seems kind of overly complex. Unfortunately that’s overly simple – since a hash function discards some information, hash tables don’t just work on hashes, they also need … Read more
To make something the key of a HashMap, you need to satisfy 3 traits: Hash — How do you calculate a hash value for the type? PartialEq — How do you decide if two instances of a type are the same? Eq — Can you guarantee that the equality is reflexive, symmetric, and transitive? This … Read more
To the contrary of what many people think, the main issue with multi-threading and HashMaps is not just a duplicate entry or a vanishing one… As you said, an infinite loop might occur when two or multiple Threads concurrently decide to resize the HashMap. If the size of the HashMap passes a given threshold, several … Read more
NSDictionary is a class cluster (see the “Class Cluster” section in The Cocoa Fundamentals Guide), meaning that the actual implementation is hidden from you, the API user. In fact, the Foundation framework will choose the appropriate implementation at run time based on amount of data etc. In addition, NSDictionary can take any id as a … Read more
A hashtable[1] is in principle the fastest way. You could however compile a Perfect Hash Function given the fact that you know the full domain ahead of time. With a perfect hash, there need not be a collision, so you can store the hash table in a linear array! With proper tweaking you can then … Read more