Java – Difference between HashMap, LinkedHashMap and TreeMap

javamap

What is the difference between HashMap, LinkedHashMap and TreeMap in Java?
I don't see any difference in the output as all the three has keySet and values. What are Hashtables?

Map m1 = new HashMap();
m1.put("map", "HashMap");
m1.put("schildt", "java2");
m1.put("mathew", "Hyden");
m1.put("schildt", "java2s");
print(m1.keySet()); 
print(m1.values()); 

SortedMap sm = new TreeMap();
sm.put("map", "TreeMap");
sm.put("schildt", "java2");
sm.put("mathew", "Hyden");
sm.put("schildt", "java2s");
print(sm.keySet()); 
print(sm.values());

LinkedHashMap lm = new LinkedHashMap();
lm.put("map", "LinkedHashMap");
lm.put("schildt", "java2");
lm.put("mathew", "Hyden");
lm.put("schildt", "java2s");
print(lm.keySet()); 
print(lm.values());

Best Answer

I prefer visual presentation:

Property HashMap TreeMap LinkedHashMap
Iteration Order no guaranteed order, will remain constant over time sorted according to the natural ordering insertion-order
Get / put / remove / containsKey O(1) O(log(n)) O(1)
Interfaces Map NavigableMap, Map, SortedMap Map
Null values/keys allowed only values allowed
Fail-fast behavior Fail-fast behavior of an iterator cannot be guaranteed, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification Fail-fast behavior of an iterator cannot be guaranteed, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification Fail-fast behavior of an iterator cannot be guaranteed, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification
Implementation buckets Red-Black Tree double-linked buckets
Is synchronized implementation is not synchronized implementation is not synchronized implementation is not synchronized
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