real time use case of treemap and hashmap? [duplicate] - java

This question already has answers here:
What is the difference between a HashMap and a TreeMap? [duplicate]
(8 answers)
Difference between HashMap, LinkedHashMap and TreeMap
(17 answers)
Closed 6 years ago.
In real time project, when we go for HashMap and TreeMap?
In what condition, we choose both?
There are also different data structure in Java Collection, so, what's the reason to use TreeMap or HashMap? and any short example?

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I want to have a big ArrayList, so its index would go beyond int, how or what can I use for that?
I already checked that Vector does have the same issue, any ideas?

What is very faster, normal for loop or foreach loop in java? [duplicate]

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What is very faster, normal {for loop} or {foreach loop} in java ?
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How to sort a map on map values [duplicate]

This question already has answers here:
Sorting HashMap by values [duplicate]
(12 answers)
Closed 9 years ago.
I have a java Map
Map<String , String>
The map is like following
olah : 3
vola : 2
sola : 5
jingle : 9
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I also want to know what difference it will make if i put a map with same values but
like
Map<String , long>
Does it improve any performance...?
See: Sort a Map<Key, Value> by values (Java)
Something like
Map<String , long>
is not possible because Java Collections can not store primitive types. If you want to do that, you can use fastutil http://fastutil.di.unimi.it/ or trove http://trove.starlight-systems.com/. Memory consumption will be better, since no Long objects are created.

Generating Unique Random ArrayList of values in Java [duplicate]

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Generating Unique Random Numbers in Java
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What would be the best way to generate 50,000 unique random values which are put into an ArrayList in Java?
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How to Remove Duplicate entries from an array in Android [duplicate]

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Java Remove Duplicates from an Array?
String={3333,4444,5555,5555,1111}
Using Delimiter i have put the String values in an array[]..
Now, How can i remove the same entries in an Array???
Use Set instead, Or use temporarily Set and get the unique result back to array
See
What interface in Java can I use to store unique objects?

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