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How to iterate through nested java collections using lambda [closed]

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I read through several threads about operating on the nested java collections using Lambda but none addressed my specific situation, although this one came close and then took off to a different direction (flatMap). Please show me how to write the following code in Lambda.
for(AppUser user : users){
List<CustomerOrder> orders = user.getOrders();
for(CustomerOrder order : orders){
order.setConsumer(user);
List<LineItem> items = order.getLineItems();
for (LineItem item : items){
item.setOrder(order);
}
}
}
Thanks

If all you want to do is iterate, the forEach method on either the Stream.java or the Iterable.java should be enough. Here is the "streamy" way of doing what you are trying to do with the for loops
users.stream().forEach( user ->
user.getOrders().stream().forEach( order -> {
order.setConsumer(user);
order.getLineItems().stream().forEach(
lineItem -> lineItem.setOrder(order)
);
}
));
Although you don't really need to convert the iterable returned by by those getters to streams.

This is a solution I came up with but I see that Smarth Ktyal already posted an answer.
users
.stream()
.forEach(e->e.getOrders()
.stream()
.forEach(k->{
k.setConsumer(e);
k.getLineItems()
.stream()
.forEach(l->l.setOrder(k));
}
)
);

Why stream() doesn't work from just declared Array [closed]

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It's probably sth simple, but I can't find answers why I can't start stream straight after creating List using Arrays.asList. 'list' is working fine, but 'list2' doesn't, no help from IntelliJ
List<Book> list = Arrays.asList(lalka,dziady,chlopi,jutrzenka);
list.stream()
.map((Book var)-> var.getAuthor().getName())
.forEach(var-> System.out.println(var));
List<Book> list2 = Arrays.asList(lalka, dziady).stream()
.map((Book var) -> var.getAuthor().getName())
.forEach(var-> System.out.println(var));

Your stream pipeline doesn't return anything (the terminal operation forEach has a void return type) so you can't assign it to a List variable.
You can write:
Arrays.asList(lalka, dziady)
.stream()
.map((Book var) -> var.getAuthor().getName())
.forEach(var-> System.out.println(var));

You're trying to assign result of .forEach to a List<Book> list2 variable.
.forEach(...) is of type void.
Remove this unnecessary assignment.

The problem is with the assignment to List list2.
You'll probably be getting an error that you cannot convert void to list
as .forEach() does not return anything.
Remove the assignment to list2 and this compiles and runs just fine.

RegEx for filtering java HashMap keys [closed]

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Closed 3 years ago.
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I'm trying to filter as HashMap of String/Int by they key, matching on a RegEx
Map<String, Integer> files = new HashMap<>();
files.put("TEST_SALES1212312.zip", 1212312);
files.put("TEST_SALES9846545.zip", 9846545);
files.put("TEST_INVENTORY2153516.zip", 2153516);
files.put("TEST_INVENTORY3651321.zip", 3651321);
String regex = "(TEST_SALES|.)+(.zip)";
List<Map.Entry<String, Integer>> matches = files.entrySet().stream()
.filter(x -> x.getKey().matches(regex))
.sorted(Map.Entry.comparingByValue())
.collect(Collectors.toList());
matches.forEach(x -> System.out.println(x.getKey()));
I tested on RegEx Tester and it correctly filtered the inventory items out. However, the above code does not filter any items.
How do I solve this problem?

This RegEx might help you to solve your problem. It creates a target group () for numeric values of your zip files, which you can simply get using $1:
TEST_[A-Z]+([0-9]+).zip
You can escape language specific metachars using \, if necessary, such as ..
If your inputs are only limited to your exampled codes, you may reduce the regex boundaries, if you wish, such as this RegEx, and it might still match:
[A-Z_]+([0-9]+).zip

Convert List<Students> to Map<K, List<V>> [closed]

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My Student class has only three attributes - age, sex and name.
I have a Map like Map<String, Student> where key is an UUID string that acts as identifier for the student.
Now i want to convert this Map to another map of pattern - Map<String,List<String>>. In this map, key can be sex of the student and value would be list of UUIDs corresponding to that sex.
I can achieve this using pre-Java8 syntax, but i am trying to do this by Java8 stream API and lambda expressions. Please help with this.
What I have tried -
Map<String, Student> map;
map.entrySet().stream().collect(e -> e.getValue().getSex(), ???how to get list of keys here???)
I am able to set the key of the target map correctly, but i am struggling to set the value.

map.entrySet().stream()
.collect(Collectors.groupingBy(entry -> entry.getValue().getSex(),
Collectors.mapping(entry -> entry.getKey(), Collectors.toList())));

Java How do I compare the values in an ArrayList and that of an Hashmap [closed]

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This is my code
I have a HashMap which is <String, JLabel>
I want to loop through the HashMap and set the labels that are not in the ArrayList to visible(false). I have tried many things nothing seems to work.
Thanks a lot

HashMap<String,JLabel> map = ...
ArrayList<JLabel> list = ...
for (JLabel label : map.values())
if (!list.contains(label))
label.setVisible(false);
Relevant methods:
Map.values()
Collection.contains(object)