hashmap related questions

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());
	}

}

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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.

I see the hash values are negative though as attached which is not clear?
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

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

I don't have any stats for that sorry

http://preshing.com/20110504/hash-collision-probabilities/

enjoy.

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

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?

The best way to understand Java maps is to study the source code. e.g. java.util.HashMap

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

The bucket starts as the tail of a linked list of HashMap.Entry

8 shown in HashMapQuestions.png screenshot is bucket number or position of hash map?

Oh