开发者

Java Equivalent to Python Dictionaries

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 differ开发者_开发百科ences of using hashtables and hashmaps versus python's dictionaries?


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.


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


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.

0

上一篇:

下一篇:

精彩评论

暂无评论...
验证码 换一张
取 消

最新问答

问答排行榜