Do you wonder if your IT business is truly profitable or if you should raise your prices? Learn how to calculate your overhead burden using our free interactive tool and use it to determine the right price for your IT services. Start calculating Now!
hashmap related questions
I am checking below link on hashmap
https://www.youtube.com/watch?v=iinE6ZBNBjw
when i put 'a1' why it put in 8th bucket out of all 16 buckets rather than 1st. Why it put second element in 9th bucket.
https://www.youtube.com/watch?v=iinE6ZBNBjw
package test;
import java.util.HashMap;
public class TestHashmap {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
HashMap<String, Integer> map = new HashMap<>();
map.put("a1", 1);
map.put("a2", 2);
map.put("a3", 3);
map.put("a4", 4);
System.out.println("map--" + map);
//String str1
}
}
when i put 'a1' why it put in 8th bucket out of all 16 buckets rather than 1st. Why it put second element in 9th bucket.
Do more with
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
package test;
import java.util.HashMap;
public class TestHashmap {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
HashMap<String, Integer> map = new HashMap<>();
map.put("a1", 1);
map.put("a2", 2);
map.put("a3", 3);
map.put("a4", 4);
System.out.println("map--" + map);
String str1="abcdef";
String str2="abcdfG";
String str3="abcdefH";
System.out.println("str1 hashcodee"+str1.hashCode());
System.out.println("str2 hashcodee"+str2.hashCode());
System.out.println("str3 hashcodee"+str3.hashCode());
}
}
why the hashCode is same for str1 and str2?
map--{a1=1, a2=2, a3=3, a4=4}
str1 hashcodee-1424385949
str2 hashcodee-1424385949
str3 hashcodee-1206291387
When you say 8th bucket, how do you know its gone into the 8th bucket?
bucket is not the same as the position in the hashmap. A bucket is a collection of entries.
bucket is not the same as the position in the hashmap. A bucket is a collection of entries.
As for your second question - it is entirely possible for two different strings to have the same hashcode.
There is nothing in the contract to prevent this so collisions will occur.
Note: - don't use hashcode as a basis for equality. You should use it along with .equals().
There is nothing in the contract to prevent this so collisions will occur.
Note: - don't use hashcode as a basis for equality. You should use it along with .equals().
I see the hash values are negative though as attached which is not clear?
HashMapQuestions.png
hashNegative.png
HashMapQuestions.png
hashNegative.png
how do i know which all strings produce same hashCode value before hand like in this case str1 and str2 has same hashCode?
map--{a1=1, a2=2, a3=3, a4=4}
str1 hashcodee-1424385949
str2 hashcodee-1424385949
str3 hashcodee-1206291387
map--{a1=1, a2=2, a3=3, a4=4}
str1 hashcodee-1424385949
str2 hashcodee-1424385949
str3 hashcodee-1206291387
how do i know which all strings produce same hashCode value before hand like in this case str1 and str2 has same hashCode?Why would you need to?
As for collisions, String.hashCode uses quite a primitive hash function, by design. This is for performance reasons.
As for negativity, that's of no consequence, when it's used as it will be turned into a positive value
Why would you need to?just general curiosity.
What all single digit string, 2digit string (like AA, DC, ZX etc) , 3 digit string like (AAA, FRG,EWA etc) have same hash?
Any program for that to find? what percentage times these hash values are equal?
please advise
http://www.enterjava.com/search?updated-min=2014-01-01T00:00:00%2B05:30&updated-max=2015-01-01T00:00:00%2B05:30&max-results=10
About bucket selection i see link explained about containsKey and put methods which decides whether 9 or 8th bucket. I was not clear on that. can you please advise more that?
The put method internally uses the hashcode of the object and calculates the hash and indexFor to find the bucket number.
It has inserted in bucket 9. When you use containsKey function , it uses the hashing functionality to find the bucket number.
About bucket selection i see link explained about containsKey and put methods which decides whether 9 or 8th bucket. I was not clear on that. can you please advise more that?
When you say 8th bucket, how do you know its gone into the 8th bucket?
bucket is not the same as the position in the hashmap. A bucket is a collection of entries.
as attached i see 8. Not sure if it is position of hashmap or bucket. I guess i am thinking both as same. I wonder how bucket and position are different. please advise
HashMapQuestions.png
8 shown in HashMapQuestions.png screenshot is bucket number or position of hash map?A Map doesn't have a notion of "position" not like a List, eg. for a List you can ask, "What is the 8th element in this list?" via a List.get(8) method call. But for a Map, the entries are not ordered in any meaningful way, so you can't ask the same question and there is no method Map.get(int position) available to call on a Map.
So, I would call it bucket number 8.
Premium Content
You need an Expert Office subscription to comment.Start Free Trial