java-8

问题 'OutOfMemoryError': Usually, this error is thrown when there is insufficient space to allocate an object in the Java heap. GC (Allocation Failure): Allocation Failure” means that there is an allocation request that is bigger than the available space in young generation. Does this mean Allocation Failure will be thrown when Young generation memory is full (Minor GC) and "OutOfMemoryError" is thrown in full GC? 回答1: These could become related as far as I can tell; but they are entirely

问题 'OutOfMemoryError': Usually, this error is thrown when there is insufficient space to allocate an object in the Java heap. GC (Allocation Failure): Allocation Failure” means that there is an allocation request that is bigger than the available space in young generation. Does this mean Allocation Failure will be thrown when Young generation memory is full (Minor GC) and "OutOfMemoryError" is thrown in full GC? 回答1: These could become related as far as I can tell; but they are entirely

问题 I have a Model and a Property class with the following signatures: public class Property { public String name; public String getName() { return name; } public void setName(String name) { this.name = name; } } public class Model { private List<Property> properties = new ArrayList<>(); public List<Property> getProperties() { return properties; } } I want a Map<String, Set<Model>> from a List<Model> where the key would be the name from the Property class. How can I can I use java8 streams to

问题 I have a Model and a Property class with the following signatures: public class Property { public String name; public String getName() { return name; } public void setName(String name) { this.name = name; } } public class Model { private List<Property> properties = new ArrayList<>(); public List<Property> getProperties() { return properties; } } I want a Map<String, Set<Model>> from a List<Model> where the key would be the name from the Property class. How can I can I use java8 streams to

问题 I'm using spark-sql-2.4.1v, and I'm trying to do find quantiles, i.e. percentile 0, percentile 25, etc, on each column of my given data. As I am doing multiple percentiles, how to retrieve each calculated percentile from the results? My dataframe df : +----+---------+-------------+----------+-----------+ | id| date| revenue|con_dist_1| con_dist_2| +----+---------+-------------+----------+-----------+ | 10|1/15/2018| 0.010680705| 6|0.019875458| | 10|1/15/2018| 0.006628853| 4|0.816039063| | 10

问题 I am using spark-sql-2.4.1v with Java 8. I need to calculate percentiles such as 25,75,90 for some given data. I tried using percentile_approx() from Spark-sql to do this. But the results of percentile_approx() are not matching the fractional percentiles of excel sheet which uses PERCENTILE.INC() . Hence, I'm wondering how to fix or adjust the percentile_approx() function. Is there anyway to overwrite or write a custom function modifying percentile_approx() which calculates fractional

问题 I went through link: Is it possible in Java to check if objects fields are null and then add default value to all those attributes? and implemented the same solution as below - Note: I am using Swagger/Open API Specs (using springdoc-openapi-ui) and while making POST request all string fields are having default value as "string" which I really wanted to set it to null or space. Any quick pointer ? public static Object getObject(Object obj) { for (Field f : obj.getClass().getFields()) { f

问题 I know that a fix was made on Java 8 Build 75 https://bugs.java.com/bugdatabase/view_bug.do?bug_id=8006684 and i cannot reproduce the same problem with the code that break on version before 75 But this code is throwing the exception on Java 8-121 but not on Java 11 i want to know in which version of the Jdk was this problem solved please. A example this code was generating the problem on versions before 75 but not afterwards. public static void main(String[] args) { xxx(); } static void xxx()

问题 I am reading the implementation details of Java 8 HashMap, can anyone let me know why Java HashMap initial array size is 16 specifically? What is so special about 16? And why is it the power of two always? Thanks 回答1: The reason why powers of 2 appear everywhere is because when expressing numbers in binary (as they are in circuits), certain math operations on powers of 2 are simpler and faster to perform (just think about how easy math with powers of 10 are with the decimal system we use).

问题 I need to convert a list of ids to array of ids. I can do it in many ways but not sure which one should be used. Say, 1. ids.stream().toArray(Id[]::new) 2. ids.toArray(new Id[ids.length]) Which one is more efficient and why? 回答1: java-11 introduced Collection::toArray that has this implementation: default <T> T[] toArray(IntFunction<T[]> generator) { return toArray(generator.apply(0)); } To make it simpler in your case, it is actually doing : ids.toArray(new Id[0]) ; that is - it is not