collections

How to create Immutable List in java?

由 自古美人都是妖i 提交于 2020-04-05 11:13:12
问题 I need to convert mutable list object to immutable list. What is the possible way in java? public void action() { List<MutableClass> mutableList = Arrays.asList(new MutableClass("san", "UK", 21), new MutableClass("peter", "US", 34)); List<MutableClass> immutableList = immutateList(mutableList); } public List<MutableClass> immutateList(List<MutableClass> mutableList){ //some code here to make this beanList immutable //ie. objects and size of beanList should not be change. //ie. we cant add new

How to create Immutable List in java?

由 断了今生、忘了曾经 提交于 2020-04-05 11:11:27
问题 I need to convert mutable list object to immutable list. What is the possible way in java? public void action() { List<MutableClass> mutableList = Arrays.asList(new MutableClass("san", "UK", 21), new MutableClass("peter", "US", 34)); List<MutableClass> immutableList = immutateList(mutableList); } public List<MutableClass> immutateList(List<MutableClass> mutableList){ //some code here to make this beanList immutable //ie. objects and size of beanList should not be change. //ie. we cant add new

Spark Cassandra Connector Java API append/remove data in a collection fail

由 懵懂的女人 提交于 2020-03-26 03:16:27
问题 I am trying to append values to a column of type set, via the JAVA API. It seems that the connector disregards the type of CollectionBehavior I am setting, and always overrides the previous collection. Even when I use CollectionRemove, the value to be removed is added to the collection. I am following the example as shown in: https://datastax-oss.atlassian.net/browse/SPARKC-340?page=com.atlassian.jira.plugin.system.issuetabpanels%3Achangehistory-tabpanel I am using: spark-core_2.11 2.2.0

Why should I avoid using the increase assignment operator (+=) to create a collection

由 删除回忆录丶 提交于 2020-03-24 00:21:08
问题 The increase assignment operator ( += ) is often used in [PowerShell] questions and answers at the StackOverflow site to construct a collection objects, e.g.: $Collection = @() 1..$Size | ForEach-Object { $Collection += [PSCustomObject]@{Index = $_; Name = "Name$_"} } Yet it appears an very inefficient operation. Is it Ok to generally state that the increase assignment operator ( += ) should be avoided for building an object collection in PowerShell? 回答1: Yes, the increase assignment operator

Jsoup: sort Elements

由 为君一笑 提交于 2020-03-22 08:09:08
问题 I need to sort a Jsoup Elements container by its ownText(). What is a recommended way to accomplish that? Does convertinng it to an ArrayList first for use with a custom comparator make sense? BTW, I tried sorting it directly, as in Collections.sort(anElementsList) but the compiler complains: Bound mismatch: The generic method sort(List<T>) of type Collections is not applicable for the arguments (Elements). The inferred type Element is not a valid substitute for the bounded parameter <T

Java parallel stream: how to wait for threads for a parallel stream to finish?

由 时光怂恿深爱的人放手 提交于 2020-03-17 10:49:02
问题 So I have a list from which I obtain a parallel stream to fill out a map, as follows: Map<Integer, TreeNode> map = new HashMap<>(); List<NodeData> list = some_filled_list; //Putting data from the list into the map list.parallelStream().forEach(d -> { TreeNode node = new TreeNode(d); map.put(node.getId(), node); }); //print out map map.entrySet().stream().forEach(entry -> { System.out.println("Processing node with ID = " + entry.getValue().getId()); }); The problem with this code is that the

Java parallel stream: how to wait for threads for a parallel stream to finish?

由 大憨熊 提交于 2020-03-17 10:48:07
问题 So I have a list from which I obtain a parallel stream to fill out a map, as follows: Map<Integer, TreeNode> map = new HashMap<>(); List<NodeData> list = some_filled_list; //Putting data from the list into the map list.parallelStream().forEach(d -> { TreeNode node = new TreeNode(d); map.put(node.getId(), node); }); //print out map map.entrySet().stream().forEach(entry -> { System.out.println("Processing node with ID = " + entry.getValue().getId()); }); The problem with this code is that the

java集合框架总结（七）

由 僤鯓⒐⒋嵵緔 提交于 2020-03-02 02:18:53
一、Collections 简介 Collections 是一个操作 Set、List 和 Map 等集合的工具类 Collections 中提供了大量方法对集合元素进行排序、查询和修改等操作，还提供了对集合对象设置不可变、对集合对象实现同步控制等方法 二、相关操作 排序操作 reverse(List)：反转 List 中元素的顺序 sort(List)：根据元素的自然顺序对指定 List 集合元素按升序排序 sort(List，Comparator)：根据指定的 Comparator 产生的顺序对 List 集合元素进行排序 查找，替换 Object max(Collection)：根据元素的自然顺序，返回给定集合中的最大元素 Object max(Collection，Comparator)：根据 Comparator 指定的顺序，返回给定集合中的最大元素 Object min(Collection)：根据元素的自然顺序，返回给定集合中的最小元素 Object min(Collection，Comparator)：根据 Comparator 指定的顺序，返回给定集合中的最小元素 int frequency(Collection，Object)：返回指定集合中指定元素的出现次数 boolean replaceAll(List list，Object oldVal，Object

equals() vs compareTo() in Comparator/able (Theoretical)

由 我的未来我决定 提交于 2020-02-28 07:35:06
问题 I don,t understand Javadoc: The natural ordering for a class C is said to be consistent with equals if and only if (e1.compareTo((Object)e2) == 0) has the same boolean value as e1.equals((Object)e2) for every e1 and e2 of class C. Why should be that way? I understand that e1.equals(e2)=true should always imply e1.compareTo(e2)==0, but I cannot understand why the opposite should be true. Compareness is not equalness! 2 equal objects should be compared to zero, but 2 differents ones should be

How to Update List<Model> with jQuery in MVC 4

由 跟風遠走 提交于 2020-02-27 08:54:54
问题 I am currently trying to create a settings page using a modified Index view. The goal is that the users get all settings displayed and can change all settings within one view and save all settings using one single button . The setting should be updated using Ajax. My current approach: View: <script language="javascript"> $(function() { $('#editSettings').submit(function () { if ($(this).valid()) { $.ajax({ url: this.action, type: this.method, data: $(this).serialize(), success: function
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