collections

问题 Related to this question: Can I add a key named 'keys' to a hashtable without overriding the 'keys' member , I am actually often using the get_Keys() method as the recommended PSBase property will just move the problem. In other words, this method appears especially handy for an unknown list of directory keys in case of a solution like: Powershell Merge 2 lists Performance. The method works as expected (also on other collections, any PowerShell version and .Net Core): $Hash = @{Keys = 'MyKeys

问题 In Scala, map and set literals can be created through, for instance, val m = Map(1->"a") And the type of the reference m and the literal are both Map[Int, String] . However, scala documents show that Map is actually a trait, with abstract members that need to be implemented in order to instantiate: scala.collection.Map, scala.collection.immutable.Map, scala.collection.mutable.Map So my question is: what is the actual, concrete class that the literal Map is based on? Same question above is

问题 I'm running an example to understand the behavior of Comparator in Java. import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; class HDTV { private int size; private String brand; public HDTV(int size, String brand) { this.size = size; this.brand = brand; } public int getSize() { return size; } public void setSize(int size) { this.size = size; } public String getBrand() { return brand; } public void setBrand(String brand) { this.brand = brand; } } class

问题 I'm running an example to understand the behavior of Comparator in Java. import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; class HDTV { private int size; private String brand; public HDTV(int size, String brand) { this.size = size; this.brand = brand; } public int getSize() { return size; } public void setSize(int size) { this.size = size; } public String getBrand() { return brand; } public void setBrand(String brand) { this.brand = brand; } } class

问题 I'm running an example to understand the behavior of Comparator in Java. import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; class HDTV { private int size; private String brand; public HDTV(int size, String brand) { this.size = size; this.brand = brand; } public int getSize() { return size; } public void setSize(int size) { this.size = size; } public String getBrand() { return brand; } public void setBrand(String brand) { this.brand = brand; } } class

问题 I created an iterator() and then removed the 1st entry from the map before iterating it. I always get the 1st item returned from the iterator. But when I remove the 2nd or subsequent entries, the current iterator does not return that entry. Example of removing 1st entry from map: Map<Integer,Integer> m1 = new ConcurrentHashMap<>(); m1.put(4, 1); m1.put(5, 2); m1.put(6, 3); Iterator i1 = m1.entrySet().iterator(); m1.remove(4); // remove entry from map while (i1.hasNext()) System.out.println(

问题 I've searched for the use of @specialized in the source code of the standard library of Scala 2.8.1. It looks like only a handful of traits and classes use this annotation: Function0 , Function1 , Function2 , Tuple1 , Tuple2 , Product1 , Product2 , AbstractFunction0 , AbstractFunction1 , AbstractFunction2 . None of the collection classes are @specialized . Why not? Would this generate too many classes? This means that using collection classes with primitive types is very inefficient, because

问题 I want to find the number of common elements between two lists without eliminating duplicates. For example: input: [1, 3, 3] & [4, 3, 3] output: 2 , since the common elements are [3, 3] input: [1, 2, 3] & [4, 3, 3] output: 1 , since the common elements are [3] If I were to use the Kotlin collections intersect, the result is a set, which will prevent me from counting duplicate values. I found (for Python) this, which handles duplicates differently and this, which led me to use this

问题 I want to find the number of common elements between two lists without eliminating duplicates. For example: input: [1, 3, 3] & [4, 3, 3] output: 2 , since the common elements are [3, 3] input: [1, 2, 3] & [4, 3, 3] output: 1 , since the common elements are [3] If I were to use the Kotlin collections intersect, the result is a set, which will prevent me from counting duplicate values. I found (for Python) this, which handles duplicates differently and this, which led me to use this

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).