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I am a long time user of Python and really like the way that the dictionaries are used. They are very intuitive and easy to use. Is there a good Java equivalent to python’s dictionaries? I have heard of people using hashmaps and hashtables. Could someone explain the similarities and differences of using hashtables and hashmaps versus python’s dictionaries?
dict class is an implementation of what the Python documentation informally calls “mapping types“. Internally,
dict is implemented using a hashtable.
There are a few minor differences in syntax, and I believe the implementations are tuned slightly differently, but overall they are completely interchangeable.
The idea of dictionary and Map is similar. Both contain elements like
key1:value1, key2:value2 ... and so on
Map is implemented different ways like
put(), get() operations are similar
import java.util.HashMap; Map map = new HashMap(); // Put elements to the map map.put("Ram", new Double(3434.34)); map.put("Krishna", new Double(123.22)); map.put("Hary", new Double(1378.00)); //to get elements map.get("Krishna"); // =123.22 map.get("Hary"); // = 1378.00
See documentation of HashMap in java8 https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html
One difference between the two is that
dict has stricter requirements as to what data types can act as a key. Java will allow any object to work as a key — although you should take care to ensure that the object’s
hashCode() method returns a unique value that reflects its internal state. Python requires keys to fit its definition of hashable, which specifies that the object’s hash code should never change over its lifetime.
As far as I’m aware (I don’t actually use java) dictionaries are just another name for a hashmap/hashtable.
Grabbing code from http://www.fluffycat.com/Java/HashMaps/ it seems they are used in a very similar manner, with a bit of extra java boiler-plate.