I have a database object that has a field that contains a list of strings. I retrieve all these objects and then use the flatMap and distinct stream methods on the resulting list to get a new list that holds all possible unique values that a database object string list can contain. Next i want to make a map where
Tag: java-stream
Counting items from Map having Set as value
I have a list of items as below Now I am converting this list into here complexList gives output as Now I need to count number of values for each “capacity” giving output as I tried and it outputs I must be mistaking in understanding streams or not be using right methods. Can anyone suggest an approach or a solution?
Can Java’s Stream.collect() return null?
The JavaDoc for Stream.collect() says that it returns “the result of the reduction”. That doesn’t tell me if code like this can return null for filteredList: I would expect that if it could return null then it would return an Optional, but it doesn’t say that either. Is it documented anywhere whether Stream.collect() can return null? Answer Collector.toList() will return
What is the difference between intermediate and terminal operations?
can someone tell me What is the difference between intermediate and terminal operations for Stream? Stream operations are combined into pipelines to process streams. All operations are either intermediate or terminal ..means?. Answer A Stream supports several operations and these operations are divided into intermediate and terminal operations. The distinction between this operations is that an intermediate operation is lazy
Does the stream.spliterator() close the stream?
Does the stream.spliterator() implicitly closes the stream, or there is a need to explicitly close it afterwards? At first glance, it seems that the .spliterator() method closes the stream, but without calling stream.close(). At least if I close it straight away after the .spliterator() method is invoked, it seems not affection the spliterator operations. This question can be extended to
Java Stream filter with regex not working
hope somebody can help me. I have a ArrayList of a Invoice class. What I’m trying to get is to filter this ArrayListand find the first element which one of its properties matches with a regex. The Invoiceclass looks like this: I’m filtering with this regex (\D+) in order to find if there is any value in the orderNumproperty that
Transform List into Map using only two keys and odd or even list indexes as values – Java 8 Stream
I would like to transform list into map using as key values only two string values. Then as values just list of strings containing elements from odd or even index positions from input list. Here is old fashion code: How to transform this code into Java 8 using streams to get this result? My current messy attempt require modifying elements
Will using a parallel stream on a single-core processor be slower than using a sequential stream?
I am applying an operation to every element in a very large LinkedList<LinkedList<Double>>: On my computer (quad-core), parallel streams seem to be faster than using sequential streams: However, not every computer is going to be multi-core. My question is, will using parallel streams on a single-processor computer be noticeably slower than using sequential streams? Answer This is highly implementation specific,
How to get element index when using a stream to traverse a list?
I want to get index when traverse list use lambda. For example: EDIT: The checkBoxes = null; is just a placeholder but will be used properly once I start writing some code. Answer Here’s how I would do it. Run an IntStream over the indexes of the list. Then filter the indexes based on whether the corresponding checkbox is selected.
extract list inside a list as a single list
I’ve a two POJOs, Sample code below Controller class This returns me a list of the list: but what I want is a single list like How can I do that with Java 8 streams? I’ve tried flatMap also, but that doesn’t go well with the Object datatype of entries. Answer Consider a List<String> as a field entries in the