Java Equivalent to Python Dictionaries
Question:
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:
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.
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.
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.
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
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?
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.
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.
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.
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