arraylist | 易学教程

How to change array list to string array for using Universal Image Loader?

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问题 I am a Novice of android. I just try to learn how to use Universal Image Loader . I find that the url of the images in Universal Image Loader are set statically or preset in String[] IMAGES . But I would like to change those image from URL . So I am done with parsing the XML and try to get those data from XML Web service . However, I don't know how to change array list to string array. Can someone teach me? The xml web service code as follow: class showCategoryTask extends AsyncTask<Void,

transient 关键字

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一、transient的用途及使用方法 Java语言的关键字，变量修饰符，如果用transient声明一个实例变量，当对象存储时，它的值不需要维持。换句话来说就是，用transient关键字标记的成员变量不参与序列化过程。作用： Java的serialization提供了一种持久化对象实例的机制。当持久化对象时，可能有一个特殊的对象数据成员，我们不想用serialization机制来保存它。为了在一个特定对象的一个域上关闭serialization，可以在这个域前加上关键字transient。当一个对象被序列化的时候，transient型变量的值不包括在序列化的表示中，然而非transient型的变量是被包括进去的。用途当一个对象实现了Serilizable接口，这个对象就可以被序列化，只需要了解这个类实现了Serilizable接口，这个类的所有属性和方法都会自动序列化。而在开发过程中，我们可能要求：当对象被序列化时（写入字节序列到目标文件）时，有些属性需要序列化，而其他属性不需要被序列化，打个比方，如果一个用户有一些敏感信息（如密码，银行卡号等），为了安全起见，不希望在网络操作（主要涉及到序列化操作，本地序列化缓存也适用）中被传输，这些信息对应的变量就可以加上transient关键字。换句话说，这个字段的生命周期仅存于调用者的内存中而不会写到磁盘里持久化。所以

ArrayList与LinkList对比

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本文简要总结一下java中ArrayList与LinkedList的区别，这在面试中也是常常会问到的一个知识点。先来看一下ArrayList和LinkedList的关系是怎样的：从继承体系可以看到，ArrayList与LinkedList都是Collection接口下List接口的实现类。可谓是一对双胞胎。但由于底层数据结构的不同导致ArrayList与LinkedList有本质上的区别。 ArrayList与LinkedList的区别 ArrayList: ArrayList是基于动态数组的数据结构。因为是数组，所以ArrayList在初始化的时候，有初始大小10 ，插入新元素的时候，会判断是否需要扩容，扩容的步长是 0.5倍原容量，扩容方式是利用数组的复制，因此有一定的开销；另外，ArrayList在进行元素插入的时候，需要移动插入位置之后的所有元素，位置越靠前，需要位移的元素越多，开销越大，相反，插入位置越靠后的话，开销就越小了，如果在最后面进行插入，那就不需要进行位移； LinkedList: 内部使用基于链表的数据结构实现存储，LinkedList有一个内部类作为存放元素的单元，里面有三个属性，用来存放元素本身以及前后2个单元的引用，另外LinkedList内部还有一个header属性，用来标识起始位置

ArrayList toArray() conversion doesn't let you use lenth()? [duplicate]

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问题 This question already has answers here : How can I get the size of an array, a Collection, or a String in Java? (2 answers) Closed 5 years ago . import java.util.*; class Ball{ public static void main(String args[]) { ArrayList al = new ArrayList(); al.add(new Integer(1)); al.add(new Integer(2)); al.add(new Integer(3)); Object a[]= al.toArray(); for (int i=0; i<a.length; i++) { System.out.println("Contents are :"+ a[i]); } }} So I created an ArrayList and added a couple of elements to it.

why is my arraylist out of bounds (index 3, size 3) when I call this method

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问题 I'm trying to find a book in an arraylist of books by using the book's name. When I try to add a book that's not in the book arraylist, it gives me the arrayoutofbounds exception index:3, size:3.... how can I fix that ? public Book findBookByName(String bookNameToFind) { boolean found = false; String bookName; int index = 0; while(!found) { bookName = bookLibrary.get(index).getTitle(); if(bookName.equals(bookNameToFind)) { found = true; } else { index++; } } return bookLibrary.get(index); 回答1

how to get unique items from the Arraylist, preserving the natural order

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问题 For example ArrayList : Integer[] intArray = new Integer[] { 0, 1 , 0 , 2 , 3 , 3 , 5 , 6 , -4 ,6 }; ArrayList<Integer> list = new ArrayList<Integer>(Arrays.asList(intArray)); need to get non-repeating values, preserving order 1 , 2 , 5 , -4 0, 3 and 6 are removed because they occur more than once. 回答1: Put the elements into a LinkedHashSet ; if you find an element that's already present, put it into another set; remove all the "already present" elements at the end: LinkedHashSet<Integer> set

concurrent modification on arraylist

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问题 There are a lot of concurrent mod exception questions, but I'm unable to find an answer that has helped me resolve my issue. If you find an answer that does, please supply a link instead of just down voting. So I originally got a concurrent mod error when attempting to search through an arraylist and remove elements. For a while, I had it resolved by creating a second arraylist, adding the discovered elements to it, then using removeAll() outside the for loop. This seemed to work, but as I

Sort ArrayList of objects through one of its instance variables

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问题 Helllo, I have an ArrayList of OBJECTS (teams). They are football teams and I would like to sort them out through their points. Obviously I am fully aware ArrayLists are sorted via the order they are inserted. But I have a TEAM class that has gamesWon, gamesLost, gamesTied and points based on a match result. I have everything ready but figured that sorting out an ArrayList through it's points would be a cool feature to make. I have read the Collections.sort(myArrayList) online, but this sorts

ArrayList looping

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问题 In Booking menu, i have main with 3 options:a,b and c. Option 'a' - selection of room types. 5 different room types to choose from. Option 'b'- selection of add-ons for each room.Each add-on can be selected for additional cost. Option 'c' - return from make booking page to main page My program needs to display 5 different types of room. At this point customer is only allowed to select option 'a', 'b' or 'c'. If customer enters and invalid number which is not 1 to 5 inclusive when selecting

Java集合List、Set、Map

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集合是 java 基础中非常重要的一部分，同样也是 Java 面试中很重要的一个知识点。所以，给王小整理了这篇关于集合的文章。 1、接口继承关系以及实现集合类存放于 Java.util 包中，主要有 3 种：set、list 和 map。 Collection：Collection 是集合 List、Set、Queue 的最基本的接口 Iterator：迭代器，可以通过迭代器遍历集合中的数据 Map：是映射表的基础接口层次关系图： 2、List Java 的 List 是非常常用的数据类型。List 是有序的 Collection。Java List 一共三个实现类：分别是 ArrayList、Vector 和 LinkedList。 2.1、ArrayList ArrayList 是最常用的 List 实现类，内部是通过数组实现的，它允许对元素进行快速随机访问。数组的缺点是每个元素之间不能有间隔，当数组大小不满足时需要增加存储能力，就要将已经有数组的数据复制到新的存储空间中。当从 ArrayList 的中间位置插入或者删除元素时，需要对数组进行复制、移动、代价比较高。因此，它适合随机查找和遍历，不适合插入和删除。 2.2、Vector Vector 与 ArrayList 一样，也是通过数组实现的，不同的是它支持线程的同步，即某一时刻只有一个线程能够写 Vector

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