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?
Answers:
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Method 1
Python’s dict class is an implementation of what the Python documentation informally calls “mapping types“. Internally, dict is implemented using a hashtable.
Java’s HashMap class is an implementation of the Map interface. Internally, HashMap 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.
Method 2
The idea of dictionary and Map is similar. Both contain elements like
key1:value1, key2:value2 ... and so on
In Java, Map is implemented different ways like HashMap, or TreeMap etc. 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
Method 3
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.
Method 4
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.
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