collectors Questions
4
Solved
I want to be able to convert a List to a HashMap where the key is the elementName and the values is a list of something random (in this case its the Element Name). So in short I want (A->List(A)...
Yaakov asked 23/7, 2014 at 17:27
14
Solved
Collectors.toMap throws a NullPointerException if one of the values is null. I don't understand this behaviour, maps can contain null pointers as value without any problems. Is there a good reason ...
Khelat asked 8/7, 2014 at 11:44
2
Solved
I have a list of orders and I want to group them by user using Java 8 stream and Collectors.groupingBy:
orderList.stream().collect(Collectors.groupingBy(order -> order.getUser())
This return ...
Rundlet asked 14/6, 2016 at 14:57
14
Solved
I have this list (List<String>):
["a", "b", null, "c", null, "d", "e"]
And I'd like something like this:
[["a", "b"], ["c"], ["d", "e"]]
In other words I want to split my list in sublis...
Electronegative asked 17/3, 2015 at 9:52
4
Solved
I have a Map<String, List<String>>. I want to transform this map to a List after filtering on the map's key.
Example:
Map<String, List<String>> words = new HashMap<>...
Lees asked 18/7, 2017 at 21:13
4
Solved
JDK 16 now includes a toList() method directly on Stream instances. In previous Java versions, you always had to use the collect method and provide a Collector instance.
The new method is obviously...
Soul asked 30/1, 2021 at 15:44
8
Solved
In Java 8, this works:
Stream<Class> stream = Stream.of(ArrayList.class);
HashMap<Class, List<Class>> map = (HashMap)stream.collect(Collectors.groupingBy(Class::getSuperclass));
...
Raised asked 25/3, 2014 at 3:45
5
Solved
I was trying to convert a list of Integers into a string of comma-separated integers.
Collectors.joining(CharSequence delimiter) - Returns a Collector that concatenates the input elements, separate...
Geotaxis asked 22/8, 2019 at 4:34
10
Solved
I know how to "transform" a simple Java List from Y -> Z, i.e.:
List<String> x;
List<Integer> y = x.stream()
.map(s -> Integer.parseInt(s))
.collect(Collectors.toList(...
Moresque asked 18/9, 2014 at 2:14
1
How can the following method be written using Java Stream API?
public Map<String, String> getMap() {
Map<String, String> mapB = new HashMap<>();
for (String parameterKey : lis...
Rhine asked 17/10, 2022 at 14:4
4
In Java Streams - what is the difference between stream.max(Comparator) and stream.collect(Collectors.maxBy(Comparator)) in terms of performance. Both will fetch the max based on the comparator bei...
Genesis asked 29/9, 2018 at 18:24
8
Solved
Let consider a hashmap
Map<Integer, List> id1 = new HashMap<Integer,List>();
I inserted some values into both hashmap.
For Example,
List<String> list1 = new ArrayList<String&g...
Platina asked 14/4, 2015 at 10:54
3
Solved
I have an Item class which contains a code, quantity and amount fields, and a list of items which may contain many items (with same code). I want to group the items by code and sum up their quantit...
Nuthouse asked 17/9, 2022 at 14:27
3
I have a stream of objects which I would like to collect the following way.
Let's say we are handling forum posts:
class Post {
private Date time;
private Data data
}
I want to create a list whi...
Phocis asked 22/12, 2015 at 13:42
6
Solved
I have an array of arrays of two strings.
var array = new String[][]{
{"a", "1"},
{"a", "2"},
{"b", "3"},
...
};
How can I collect t...
Johannisberger asked 3/5, 2022 at 5:38
1
Solved
I am trying to implement a simple collector, which takes a list of collectors and simultaneously collects values in slightly different ways from a stream.
It is quite similar to Collectors.teeing, ...
Waverley asked 6/2, 2022 at 11:5
4
Solved
i was having working code with earlier version of java 8 which i was using to get unique values from list but since i upgraded to JDK 66 its giving me an error
Type mismatch: cannot convert from ...
Magnetics asked 25/1, 2016 at 10:5
2
Solved
I've a two POJOs,
Sample code below
class A {
String name;
Object entries; // this can be a List<String> or a string - hence Object datatype
//getters and setter here
}
class B {
int s...
Hash asked 27/4, 2017 at 6:30
5
Solved
Suppose I have a group of bumper cars, which have a size, a color and an identifier ("car code") on their sides.
class BumperCar {
int size;
String color;
String carCode;
}
Now I need...
Plumbery asked 18/1, 2019 at 12:29
3
In java 8 , Stream API help us to do our job with very clean and with less number of code. I am big fan of these stream API. But there are few operations which kind of help in solving the sam...
Additory asked 16/6, 2021 at 8:11
7
If I have collections Point , how do I compute average of x,y using Java 8 stream on a single iteration.
Following example creates two stream & iterates twice on the input collection to compu...
Lacker asked 13/1, 2015 at 15:35
1
Solved
I have this list of data
List<Status> statuses = [
{
id: 123
mainSatus: HA
MoreInfo: {
name: max
status: MM
}
},
{
id: 456
mainSatus: HA
MoreInfo: {
name: max
status: KK
}
},
...
Bernete asked 27/5, 2021 at 9:14
2
Solved
I have a class CarPart defined as:
class CarPart {
String name;
BigDecimal price;
Supplier supplier;
}
A class Report:
class Report {
List<Part> parts;
BigDecimal total;
}
and a class ...
Rooky asked 20/5, 2021 at 16:52
7
This is really a question about a minor detail, but I'm under the impression to get something wrong here. If you add duplicate keys using Collectors.toMap-method it throws an Exception with message...
Nork asked 14/10, 2016 at 9:27
4
Solved
We have a Student class as follows:
class Student {
private int marks;
private String studentName;
public int getMarks() {
return marks;
}
public void setMarks(int marks) {
this.marks = ma...
Gerda asked 20/1, 2019 at 7:21
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