arraylist

问题 What does it mean when we say an ArrayList is not synchronized? Does it mean that if we declare an ArrayList in object scope, multiple threads accessing the objects have the opportunity to modify the list? 回答1: What does it mean when we say an ArrayList is not synchronized? It means that accessing an ArrayList instance from multiple threads may not be safe (read, "may result in unexpected behavior" or "may not work as advertised"). Further reading: Synchronization and thread safety in Java

问题 How can I initialize a multidimensional List statically? This works: List<List<Integer>> list = new ArrayList<List<Integer>>(); But I'd like to init the list with some static lists like: (1,2,3), (4,5,6) and (7,8,9) 回答1: If you create a helper method, the code looks a bit nicer. For example public class Collections { public static <T> List<T> asList(T ... items) { List<T> list = new ArrayList<T>(); for (T item : items) { list.add(item); } return list; } } and then you can do (with a static

问题 Following is my code used to sort a list with predefined order. Defined order is mentioned in itemsSorted list. final List<String> itemsSorted = myMethod.getSortedItems(); List<String> plainItemList = myMethod2.getAllItems(); final Comparator<String> comparator = new Comparator<String>() { public int compare(String str1, String str2) { return orderOf(str1) - orderOf(str2); } private int orderOf(String name) { return ((itemsSorted)).indexOf(name); } }; Collections.sort(plainItemList,

问题 I have a class called Hand and another class to test it. Hand uses global variables and change their values with some methods if in class test I create two variables of the Hand class changes in one of the variables will affect the other. How can I make them separate ? Class Hand : private static List<Card> hand = new ArrayList<Card>(); Class Test : Hand hand1 = new Hand(); Hand hand2 = new Hand(); If I add values to hand1 arraylist it changes also the values of hand2 arraylist. Can I

问题 I have a class called Hand and another class to test it. Hand uses global variables and change their values with some methods if in class test I create two variables of the Hand class changes in one of the variables will affect the other. How can I make them separate ? Class Hand : private static List<Card> hand = new ArrayList<Card>(); Class Test : Hand hand1 = new Hand(); Hand hand2 = new Hand(); If I add values to hand1 arraylist it changes also the values of hand2 arraylist. Can I

问题 import java.util.ArrayList; import java.util.Random; public class College { // instance variables - replace the example below with your own private ArrayList<Student> students; public College() { // initialise instance variables ArrayList<Student> students = new ArrayList<Student>(); students.add("Student 1"); students.add("Student 2"); students.add("Student 3"); } } basically it highlights the .add showing the error message "java.lang.IllegalArgumentException: bound must be positive", I don

问题 import java.util.ArrayList; import java.util.Random; public class College { // instance variables - replace the example below with your own private ArrayList<Student> students; public College() { // initialise instance variables ArrayList<Student> students = new ArrayList<Student>(); students.add("Student 1"); students.add("Student 2"); students.add("Student 3"); } } basically it highlights the .add showing the error message "java.lang.IllegalArgumentException: bound must be positive", I don

问题 So I have a database with players names and their skill level. It looks like this: Id | Name | Level 1 | Peter | 24 2 | Andy | 23 ... 24 | John | 1 The first player in the list with the highest level is the strongest one, and the last is the weakest. I need to sort them in groups with 4 players, so if I have 24 people there will be 6 groups. The way I need to sort it I call "zig-zag". It goes like this: Ag Bg Cg Dg Eg Fg 01 02 03 04 05 06 12 11 10 09 08 07 13 14 15 16 17 18 24 23 22 21 20 19

问题 So I have a database with players names and their skill level. It looks like this: Id | Name | Level 1 | Peter | 24 2 | Andy | 23 ... 24 | John | 1 The first player in the list with the highest level is the strongest one, and the last is the weakest. I need to sort them in groups with 4 players, so if I have 24 people there will be 6 groups. The way I need to sort it I call "zig-zag". It goes like this: Ag Bg Cg Dg Eg Fg 01 02 03 04 05 06 12 11 10 09 08 07 13 14 15 16 17 18 24 23 22 21 20 19

问题 I am wondering what is the time complexity [in big O(n) notations] of ArrayList to Array conversion: ArrayList assetTradingList = new ArrayList(); assetTradingList.add("Stocks trading"); assetTradingList.add("futures and option trading"); assetTradingList.add("electronic trading"); assetTradingList.add("forex trading"); assetTradingList.add("gold trading"); assetTradingList.add("fixed income bond trading"); String [] assetTradingArray = new String[assetTradingList.size()]; assetTradingArray