java - Difference between HashMap, LinkedHashMap and TreeMap

Question

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());

Answer 1

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