arraylist

What's Wrong with an ArrayList?

由 霸气de小男生 提交于 2019-12-28 03:05:09
问题 Recently I asked a question on SO that had mentioned the possible use of an c# ArrayList for a solution. A comment was made that using an arraylist is bad. I would like to more about this. I have never heard this statement before about arraylists. could sombody bring me up to speed on the possible performance problems with using arraylists c#. .net-2 回答1: The main problem with ArrayList is that is uses object - it means you have to cast to and from whatever you are encapsulating. It is a

What's Wrong with an ArrayList?

由 那年仲夏 提交于 2019-12-28 03:05:09
问题 Recently I asked a question on SO that had mentioned the possible use of an c# ArrayList for a solution. A comment was made that using an arraylist is bad. I would like to more about this. I have never heard this statement before about arraylists. could sombody bring me up to speed on the possible performance problems with using arraylists c#. .net-2 回答1: The main problem with ArrayList is that is uses object - it means you have to cast to and from whatever you are encapsulating. It is a

Scanner skipping every second line from file [duplicate]

由 你离开我真会死。 提交于 2019-12-28 02:18:07
问题 This question already has answers here : Scanner is skipping nextLine() after using next() or nextFoo()? (17 answers) How to use java.util.Scanner to correctly read user input from System.in and act on it? (1 answer) Closed last year . I'm trying to scan a text file and place each line into an arraylist, and stop scanning when the next line is a '*', however, my arraylist is storing every 2nd line and I am not sure why. Scanner scan = new Scanner(new File("src/p/input2.txt")); ArrayList

JAXB: How to marshal objects in lists?

由 时光总嘲笑我的痴心妄想 提交于 2019-12-28 01:50:13
问题 Perhaps a stupid question: I have a List of type <Data> which I want to marshal into a XML file. This is my class Database containing an ArrayList ... @XmlRootElement public class Database { List<Data> records = new ArrayList<Data>(); public List<Data> getRecords() { return records; } public void setRecords(List<Data> records) { this.records = records; } } ...and this is class Data: // @XmlRootElement public class Data { String name; String address; public String getName() { return name; }

Best way to create a hashmap of arraylist

由 谁说我不能喝 提交于 2019-12-27 17:38:26
问题 I have one million rows of data in .txt format. the format is very simple. For each row: user1,value1 user2,value2 user3,value3 user1,value4 ... You know what I mean. For each user, it could appear many times, or appear only once (you never know). I need to find out all the values for each user. Because user may appear randomly, I used Hashmap to do it. That is: HashMap(key: String, value: ArrayList). But to add data to the arrayList, I have to constantly use HashMap get(key) to get the

Best way to create a hashmap of arraylist

由 天涯浪子 提交于 2019-12-27 17:38:07
问题 I have one million rows of data in .txt format. the format is very simple. For each row: user1,value1 user2,value2 user3,value3 user1,value4 ... You know what I mean. For each user, it could appear many times, or appear only once (you never know). I need to find out all the values for each user. Because user may appear randomly, I used Hashmap to do it. That is: HashMap(key: String, value: ArrayList). But to add data to the arrayList, I have to constantly use HashMap get(key) to get the

Get specific ArrayList item

由 余生长醉 提交于 2019-12-27 13:05:13
问题 public static ArrayList mainList = someList; How can I get a specific item from this ArrayList ? mainList[3] ? 回答1: As many have already told you: mainList.get(3); Be sure to check the ArrayList Javadoc. Also, be careful with the arrays indices: in Java, the first element is at index 0 . So if you are trying to get the third element, your solution would be mainList.get(2); 回答2: Time to familiarize yourself with the ArrayList API and more: ArrayList at Java 6 API Documentation For your

java核心数据结构总结

由 こ雲淡風輕ζ 提交于 2019-12-27 11:02:31
　　JDK提供了一组主要的数据结构的实现，如List、Set、Map等常用结构，这些结构都继承自java.util.collection接口。 List接口 　　List有三种不同的实现，ArrayList和Vector使用数组实现，其封装了对内部数组的操作。LinkedList使用了循环双向链表的数据结构，LinkedList链表是由一系列的链表项连接而成，一个链表项包括三部分：链表内容、前驱表项和后驱表项。 　　LinkedList的表项结构如图： 　　LinkedList表项间的连接关系如图： 　　 　　可以看出，无论LinkedList是否为空，链表都有一个header表项，它即表示链表的开头也表示链表的结尾。表项header的后驱表项便是链表的第一个元素，其前驱表项就是链表的最后一个元素。 　　对基于链表和基于数组的两种List的不同实现做一些比较： 　　1、增加元素到列表的末尾： 　　在ArrayList中源代码如下： 1 public boolean add(E e) { 2 ensureCapacityInternal(size + 1); // Increments modCount!! 3 elementData[size++] = e; 4 return true; 5 } 　　add()方法性能的好坏取决于grow()方法的性能： 1 private

How to sort an ArrayList using multiple sorting criteria?

由 拟墨画扇 提交于 2019-12-27 10:41:29
问题 I have an array list that contains Quote objects. I want to be able to sort alphabetically by name, by change, and by percent change. How can I sort my arraylist? package org.stocktwits.model; import java.io.Serializable; import java.text.DecimalFormat; public class Quote implements Serializable { private static final long serialVersionUID = 1L; public String symbol; public String name; public String change; public String percentChange; public String open; public String daysHigh; public

How to sort an ArrayList using multiple sorting criteria?

由 孤街浪徒 提交于 2019-12-27 10:40:48
问题 I have an array list that contains Quote objects. I want to be able to sort alphabetically by name, by change, and by percent change. How can I sort my arraylist? package org.stocktwits.model; import java.io.Serializable; import java.text.DecimalFormat; public class Quote implements Serializable { private static final long serialVersionUID = 1L; public String symbol; public String name; public String change; public String percentChange; public String open; public String daysHigh; public
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