java-8

问题 regarding the following code: public class Test <T extends Comparable>{ public static void main(String[] args){ List<String> lst = Array.asList("abc","def"); System.out.println(func(lst)); } public static boolean func(List<**here**> lst){ return lst.get(0).compareTo(lst.get(1)) == 0; } } why writing " ? extends Comparable" here would compile , and writing "Comparable" would not compile? thanks in advance. 回答1: This happens because generics are invariant . Even if String is a Comparable ,

问题 Is this statement true that Java 8 provides functional style but is not functional programming as the syntax which it uses is also an object? Calculator calc = (i, j) -> i/j; If yes, then why we get articles everywhere Functional Programming with Java 8? 回答1: Here is a (non-exhaustive) list of abstract FP concepts: Focus on immutability Referential transparency for functions Limitations on side effects (follows from 1 & 2) Expression-based, no statements. Statements are not first-class.

问题 Below is my code to upload some file attachments to external storage. I would like to know if there is a way to avoid for loop in the below method to iterate over the MultipartFile[] array so that everything will be done using the java streams and lambda functions. Would like to have any better way to achieve the below public void uploadMyFiles(MultipartFile[] multipartFiles, String path) throws Exception { ConcurrentHashMap<String, String> sMap = new ConcurrentHashMap<>(); ExecutorService

问题 I am fetching datetime from oracle db and parsing in java-11 using ZonedDateTime as below: oracle --> 1/19/2020 06:09:46.038631 PM java ZonedDateTime 0/p --> 2020-01-19T18:09:46.038631Z[UTC] oracle --> 1/19/2011 4:00:00.000000 AM java ZonedDateTime o/p --> 2011-01-19T04:00Z[UTC] (So, here the 0s are truncated by default. However, my requirement is to have consistent fixed length o/p like #1.) expected java ZonedDateTime o/p --> 2011-01-19T04:00:00.000000Z[UTC] However, I didnt find any date

问题 This question already has answers here : How to get start and end range from list of timestamps? (2 answers) Date year value showing valid when invalid [duplicate] (3 answers) Closed 2 years ago . I'm in the process of changing our existing SimpleDateFormat based code to use the new Java 8 LocalDateTime and ZonedDateTime classes. I couldn't find an easy way to convert this piece. Considering sample date and format. String testDate = "2012-12-31T10:10:10-06:00"; String testFormat = "yyyy-MM-dd

问题 This question already has answers here : How to get start and end range from list of timestamps? (2 answers) Date year value showing valid when invalid [duplicate] (3 answers) Closed 2 years ago . I'm in the process of changing our existing SimpleDateFormat based code to use the new Java 8 LocalDateTime and ZonedDateTime classes. I couldn't find an easy way to convert this piece. Considering sample date and format. String testDate = "2012-12-31T10:10:10-06:00"; String testFormat = "yyyy-MM-dd

问题 My current date: Date utc: 2018-06-06T16:30:00Z (ISO 8601 in UTC) OR Date iso: 2018-06-06T11:30:00-05:00 (ISO 8601) OR Date epoch: 1528302600000 (Epoch/Unix Timestamp) I wish to convert the above DateTime to some another time zone areas (like GMT+5:30). And I'm not sure which time format I'll receive from above three. So can I've a generic method which can convert above to some another time zone returning java.util.Date in Java 8? I did Something like this, But it didn't worked out public

问题 Requirement is to get all the matching and non matching records from the List of Map using multiple matching criteria using the streams. i.e Instead of having a single filter to compare only "Email", required to compare two list for matching records with multiple filter predicate for comparing Email and Id both. List1: [{"Email","naveen@domain.com", "Id": "A1"}, {"Email":"test@domain.com","id":"A2"}] List2: [{"Email","naveen@domain.com", "Id": "A1"}, {"Email":"test@domain.com","id":"A2"}, {

问题 Other technologies I know (.Net, JS) contain the simplest fold/reduce operation: TResult reduce(TResult result, (TResult prevResult, TValue value) -> TResult) One method I found requires TValue and TResult to be the same type. Other one requires providing BinaryOperation that combines 2 TResults. None of those constraints matches my context. For now I ended up with code like: Accumulator acc = someInitialValue; for(Element element: list) { accumulator = reducer(accumulator, element); } but I

问题 Other technologies I know (.Net, JS) contain the simplest fold/reduce operation: TResult reduce(TResult result, (TResult prevResult, TValue value) -> TResult) One method I found requires TValue and TResult to be the same type. Other one requires providing BinaryOperation that combines 2 TResults. None of those constraints matches my context. For now I ended up with code like: Accumulator acc = someInitialValue; for(Element element: list) { accumulator = reducer(accumulator, element); } but I