java-8

问题 I have a requirement for parsing ISO8601 formatted strings in Java with various levels of accuracy. Some examples of the string I need to parse are: 2018 2018-10 2018-10-15 2018-10-15T12:00 2018-10-15T12:00:30 2018-10-15T12:00:30.123 20181015 201810151200 20181015120030 20181015120030.123 20181015T12:00:30.123 Where I don't have a field then I am free to assume the lowest valid value that applies (for example, if the month is missing I can assume January, if the day is missing then assume the

问题 I have a requirement for parsing ISO8601 formatted strings in Java with various levels of accuracy. Some examples of the string I need to parse are: 2018 2018-10 2018-10-15 2018-10-15T12:00 2018-10-15T12:00:30 2018-10-15T12:00:30.123 20181015 201810151200 20181015120030 20181015120030.123 20181015T12:00:30.123 Where I don't have a field then I am free to assume the lowest valid value that applies (for example, if the month is missing I can assume January, if the day is missing then assume the

问题 I've below requirement:- Employee.java public boolean isAdult(Integer age) { if(age >= 18) { return true; } return false; } Predicate.java private Integer age; Predicate<Integer> isAdult; public PredicateAnotherClass(Integer age, Predicate<Integer> isAdult) { this.age = age; System.out.println("Test result is "+ isAdult(age)); } public void testPredicate() { System.out.println("Calling the method defined in the manager class"); } Now My goal is to test whether the age which i pass to

问题 I'm new to Java8 and I can't use streams to map one array into another 2 dimensional array. I have one 2-dimensional array which is a pattern: boolean[][] pattern = { {true, true, false}, {true, false, true}, {false, true, true} }; And second array which contains keys. 0 means: take 0-element from pattern 1 means: take 1-element from pattern and so on int[] keys = {2, 1, 0}; From these 2 arrays I'd like to produce another 2-dimensional array. In this case the result will look like this:

问题 I have a class like this ObjectA id type where id is unique but the type can be duplicate so if I have a list of ObjectA like this (id, type) = (1, "A") , (2, "B"), (3, "C"), (4, "A") then I want Map<type, List<id>> where map is < "A",[1,4], "B",[2], "C",[3] > It is working with Java 7 but can't find a way to do it in Java 8. In Java 8 I can create key, value pair but not able to create a list if a type is same. 回答1: yourTypes.stream() .collect(Collectors.groupingBy( ObjectA::getType,

问题 I have a class like this ObjectA id type where id is unique but the type can be duplicate so if I have a list of ObjectA like this (id, type) = (1, "A") , (2, "B"), (3, "C"), (4, "A") then I want Map<type, List<id>> where map is < "A",[1,4], "B",[2], "C",[3] > It is working with Java 7 but can't find a way to do it in Java 8. In Java 8 I can create key, value pair but not able to create a list if a type is same. 回答1: yourTypes.stream() .collect(Collectors.groupingBy( ObjectA::getType,

问题 I'm retrofitting old some SimpleDateFormat code to use the new Java 8 DateTimeFormatter . SimpleDateFormat , and thus the old code, accepts strings with stuff in them after the date like "20130311nonsense". The DateTimeFormat I created throws a DateTimeParseException for these strings, which is probably the right thing to do, but I'd like to maintain compatibility. Can I modify my DateTimeFormat to accept these strings? I'm currently creating it like this: DateTimeFormatter.ofPattern(

问题 I'm retrofitting old some SimpleDateFormat code to use the new Java 8 DateTimeFormatter . SimpleDateFormat , and thus the old code, accepts strings with stuff in them after the date like "20130311nonsense". The DateTimeFormat I created throws a DateTimeParseException for these strings, which is probably the right thing to do, but I'd like to maintain compatibility. Can I modify my DateTimeFormat to accept these strings? I'm currently creating it like this: DateTimeFormatter.ofPattern(

问题 I have collection List<Foo> of Foo elements: class Foo { private TypeEnum type; private int amount; //getters, setters ... } Foo type can be TypeEnum.A and TypeEnum.B . I would like to get only those Foo elements from list which if the element have type == TypeEnum.B then amount is greater than zero ( amount > 0 ). How can I do it by Java 8 Streams filter() method? If I use: List<Foo> l = list.stream() .filter(i -> i.getType().equals(TypeEnum.B) && i.getAmount() > 0) .collect(Collectors.<Foo

问题 I am trying to calculate the sum of squares of values in the list. Below are three variations which all calculates the required value. I want to know which one is the most efficient. I am expecting the third one to be more efficient as auto boxing is only done once. // sum of squares int sum = list.stream().map(x -> x * x).reduce((x, y) -> x + y).get(); System.out.println("sum of squares: " + sum); sum = list.stream().mapToInt(x -> x * x).sum(); System.out.println("sum of squares: " + sum);