How do I get a keyset of double arrays (e.g. array[double]) from a LinkedHashMap set
I have been tackling the travelling salesperson problem for a final year module. I have been using LinkedHashMaps to store different journeys as array[double] keys so that I could pair the journeys with their journey length values.
I am using the line of code below to try and get the keys:
List<Double> keyList = new ArrayList<Double>(hmap.keySet());
But it isn't working and keeps throwing an error (Cannot resolve constructor 'ArrayList(java.util.Set<double>)'.
How do you get a key set from a LinkedHashMap set when the keys are double types?
java arrays arraylist hashmap double
edited Nov 13 '18 at 23:36
shmosel
35.8k43891
asked Nov 13 '18 at 23:35
S B BS B B
1
add a comment |
I have been tackling the travelling salesperson problem for a final year module. I have been using LinkedHashMaps to store different journeys as array[double] keys so that I could pair the journeys with their journey length values.
I am using the line of code below to try and get the keys:
List<Double> keyList = new ArrayList<Double>(hmap.keySet());
But it isn't working and keeps throwing an error (Cannot resolve constructor 'ArrayList(java.util.Set<double>)'.
How do you get a key set from a LinkedHashMap set when the keys are double types?
java arrays arraylist hashmap double
edited Nov 13 '18 at 23:36
shmosel
35.8k43891
asked Nov 13 '18 at 23:35
S B BS B B
1
1
You shouldn't use arrays as a map key.
– shmosel
Nov 13 '18 at 23:37
Why? Also, how would you represent a 4 point/digit tour in a hashMap as a key?
– S B B
Nov 13 '18 at 23:46
Arrays don't have value equality. That is,!arr.equals(arr.clone()). Either create a custom class with a properequals()implementation or use a collection type, likeList.
– shmosel
Nov 13 '18 at 23:48
The error is telling you that you can't make anArrayListofDoubleby passing the constructor aSetofdouble.Doubleis an object representing one floating point number.doubleis an array of native datatypes, each one representing one floating point number.
– MyStackRunnethOver
Nov 13 '18 at 23:57
So I'd have to convert/change the value to already be an arraylist of doubles instead of an array?
– S B B
Nov 14 '18 at 0:12
add a comment |
I have been tackling the travelling salesperson problem for a final year module. I have been using LinkedHashMaps to store different journeys as array[double] keys so that I could pair the journeys with their journey length values.
I am using the line of code below to try and get the keys:
List<Double> keyList = new ArrayList<Double>(hmap.keySet());
But it isn't working and keeps throwing an error (Cannot resolve constructor 'ArrayList(java.util.Set<double>)'.
How do you get a key set from a LinkedHashMap set when the keys are double types?
java arrays arraylist hashmap double
edited Nov 13 '18 at 23:36
shmosel
35.8k43891
asked Nov 13 '18 at 23:35
S B BS B B
1
I have been tackling the travelling salesperson problem for a final year module. I have been using LinkedHashMaps to store different journeys as array[double] keys so that I could pair the journeys with their journey length values.
I am using the line of code below to try and get the keys:
List<Double> keyList = new ArrayList<Double>(hmap.keySet());
But it isn't working and keeps throwing an error (Cannot resolve constructor 'ArrayList(java.util.Set<double>)'.
How do you get a key set from a LinkedHashMap set when the keys are double types?
java arrays arraylist hashmap double
java arrays arraylist hashmap double
edited Nov 13 '18 at 23:36
shmosel
35.8k43891
asked Nov 13 '18 at 23:35
S B BS B B
1
edited Nov 13 '18 at 23:36
shmosel
35.8k43891
asked Nov 13 '18 at 23:35
S B BS B B
1
edited Nov 13 '18 at 23:36
shmosel
35.8k43891
edited Nov 13 '18 at 23:36
shmosel
35.8k43891
edited Nov 13 '18 at 23:36
shmosel
35.8k43891
35.8k43891
asked Nov 13 '18 at 23:35
S B BS B B
1
asked Nov 13 '18 at 23:35
S B BS B B
1
asked Nov 13 '18 at 23:35
S B BS B B
1
1
1
You shouldn't use arrays as a map key.
– shmosel
Nov 13 '18 at 23:37
Why? Also, how would you represent a 4 point/digit tour in a hashMap as a key?
– S B B
Nov 13 '18 at 23:46
Arrays don't have value equality. That is,!arr.equals(arr.clone()). Either create a custom class with a properequals()implementation or use a collection type, likeList.
– shmosel
Nov 13 '18 at 23:48
The error is telling you that you can't make anArrayListofDoubleby passing the constructor aSetofdouble.Doubleis an object representing one floating point number.doubleis an array of native datatypes, each one representing one floating point number.
– MyStackRunnethOver
Nov 13 '18 at 23:57
So I'd have to convert/change the value to already be an arraylist of doubles instead of an array?
– S B B
Nov 14 '18 at 0:12
add a comment |
1
You shouldn't use arrays as a map key.
– shmosel
Nov 13 '18 at 23:37
Why? Also, how would you represent a 4 point/digit tour in a hashMap as a key?
– S B B
Nov 13 '18 at 23:46
Arrays don't have value equality. That is,!arr.equals(arr.clone()). Either create a custom class with a properequals()implementation or use a collection type, likeList.
– shmosel
Nov 13 '18 at 23:48
The error is telling you that you can't make anArrayListofDoubleby passing the constructor aSetofdouble.Doubleis an object representing one floating point number.doubleis an array of native datatypes, each one representing one floating point number.
– MyStackRunnethOver
Nov 13 '18 at 23:57
So I'd have to convert/change the value to already be an arraylist of doubles instead of an array?
– S B B
Nov 14 '18 at 0:12
1
1
You shouldn't use arrays as a map key.
– shmosel
Nov 13 '18 at 23:37
You shouldn't use arrays as a map key.
– shmosel
Nov 13 '18 at 23:37
Why? Also, how would you represent a 4 point/digit tour in a hashMap as a key?
– S B B
Nov 13 '18 at 23:46
Why? Also, how would you represent a 4 point/digit tour in a hashMap as a key?
– S B B
Nov 13 '18 at 23:46
Arrays don't have value equality. That is,
!arr.equals(arr.clone()). Either create a custom class with a proper equals() implementation or use a collection type, like List.– shmosel
Nov 13 '18 at 23:48
Arrays don't have value equality. That is,
!arr.equals(arr.clone()). Either create a custom class with a proper equals() implementation or use a collection type, like List.– shmosel
Nov 13 '18 at 23:48
The error is telling you that you can't make an
ArrayList of Double by passing the constructor a Set of double. Double is an object representing one floating point number. double is an array of native datatypes, each one representing one floating point number.– MyStackRunnethOver
Nov 13 '18 at 23:57
The error is telling you that you can't make an
ArrayList of Double by passing the constructor a Set of double. Double is an object representing one floating point number. double is an array of native datatypes, each one representing one floating point number.– MyStackRunnethOver
Nov 13 '18 at 23:57
So I'd have to convert/change the value to already be an arraylist of doubles instead of an array?
– S B B
Nov 14 '18 at 0:12
So I'd have to convert/change the value to already be an arraylist of doubles instead of an array?
– S B B
Nov 14 '18 at 0:12
add a comment |
1 Answer
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What are the data types for hmap? You can't create a List or Set of native types such as int and double. You would have to use classes like Integer or Double instead. If that isn't possible, you can create an empty keyList and loop through your keySet and add each key like this: keyList.add(Double.valueOf(hmap.keySet()[i])
answered Nov 13 '18 at 23:45
JustinJustin
9701511
add a comment |
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What are the data types for hmap? You can't create a List or Set of native types such as int and double. You would have to use classes like Integer or Double instead. If that isn't possible, you can create an empty keyList and loop through your keySet and add each key like this: keyList.add(Double.valueOf(hmap.keySet()[i])
answered Nov 13 '18 at 23:45
JustinJustin
9701511
add a comment |
What are the data types for hmap? You can't create a List or Set of native types such as int and double. You would have to use classes like Integer or Double instead. If that isn't possible, you can create an empty keyList and loop through your keySet and add each key like this: keyList.add(Double.valueOf(hmap.keySet()[i])
answered Nov 13 '18 at 23:45
JustinJustin
9701511
add a comment |
What are the data types for hmap? You can't create a List or Set of native types such as int and double. You would have to use classes like Integer or Double instead. If that isn't possible, you can create an empty keyList and loop through your keySet and add each key like this: keyList.add(Double.valueOf(hmap.keySet()[i])
answered Nov 13 '18 at 23:45
JustinJustin
9701511
What are the data types for hmap? You can't create a List or Set of native types such as int and double. You would have to use classes like Integer or Double instead. If that isn't possible, you can create an empty keyList and loop through your keySet and add each key like this: keyList.add(Double.valueOf(hmap.keySet()[i])
answered Nov 13 '18 at 23:45
JustinJustin
9701511
answered Nov 13 '18 at 23:45
JustinJustin
9701511
answered Nov 13 '18 at 23:45
JustinJustin
9701511
answered Nov 13 '18 at 23:45
JustinJustin
9701511
9701511
add a comment |
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1
You shouldn't use arrays as a map key.
– shmosel
Nov 13 '18 at 23:37
Why? Also, how would you represent a 4 point/digit tour in a hashMap as a key?
– S B B
Nov 13 '18 at 23:46
Arrays don't have value equality. That is,
!arr.equals(arr.clone()). Either create a custom class with a properequals()implementation or use a collection type, likeList.– shmosel
Nov 13 '18 at 23:48
The error is telling you that you can't make an
ArrayListofDoubleby passing the constructor aSetofdouble.Doubleis an object representing one floating point number.doubleis an array of native datatypes, each one representing one floating point number.– MyStackRunnethOver
Nov 13 '18 at 23:57
So I'd have to convert/change the value to already be an arraylist of doubles instead of an array?
– S B B
Nov 14 '18 at 0:12