A brief discussion on the difference between Arrays.asList() and ArrayList types-javaTutorial-php.cn

A brief discussion on the difference between Arrays.asList() and ArrayList types

高洛峰

Release： 2017-02-04 10:06:12

Original

2085 people have browsed it

<pre name="code" class="html">Arrays.asList()<br></p>
<p>Convert an array Converted into a List object, this method will return an ArrayList type object. This ArrayList class is not the java.util.ArrayList class, but a static internal class of the Arrays class! If you use this object to add, delete, and update the list, an UnsupportedOperationException will be reported. </p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:java;toolbar:false"><pre name="code" class="html">自己测试：<span>   </span>//arrayList
<span>        </span>List list = new ArrayList();
<span>        </span>list.add("yz_b_insert");
<span>        </span>list.add("yz_b_del");
<span>        </span>list.add("yz_b_update");
<span>        </span>list.add("yz_b_see");
<span>        </span>System.out.println(list.contains("yz_b_update")+"=="+list);
<span>        </span>//arrays.asList()
<span>        </span>String dd = "yz_b_insert,yz_b_del,yz_b_update,yz_b_see";
<span>        </span>List list2 = Arrays.asList(dd);
<span>        </span>System.out.println(list2.contains("yz_b_update")+"@@@@@"+list2);

Copy after login

contains to determine the existence of a certain string in the collection. Note that the <pre name="code" class="html">arraylist conversion is not available I cannot test it , there are experts who can give some advice The following are the resources found online <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:java;toolbar:false">为什么Arrays.asList产生的List是不可添加或者删除，否则会产生UnsupportedOperationException，就可以得到解释了。 如果我们想把一个变长或者数据转变成List，而且期望这个List能够进行add或者remove操作，那该怎么做呢？ 我们可以写一个类似的方法，里面直接采用java.util.ArrayList即可。 比如： <pre class="java" name="code" style="color: rgb(102, 102, 102); background-color: rgb(255, 255, 255);">import java.util.ArrayList; import java.util.Collections; import java.util.List; public class MyArrays { public static <T> List<T> asList(T... a) { List<T> list = new ArrayList<T>(); Collections.addAll(list, a); return list; } }

import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class Test { @SuppressWarnings("unchecked") public static void main(String[] args) { List<String> stooges = Arrays.asList("Larry", "Moe", "Curly"); print(stooges); List<List<String>> seasonsList = Arrays.asList(retrieveSeasonsList()); print(seasonsList); /* * 自己实现一个asList方法，能够添加和删除。 */ List<String> list = MyArrays.asList("Larry", "Moe", "Curly"); list.add("Hello"); print(list); } private static <T> void print(List<T> list) { System.out.println(list); } private static List<String> retrieveSeasonsList() { List<String> seasonsList = new ArrayList<String>(); seasonsList.add("Spring"); seasonsList.add("Summer"); seasonsList.add("Autumn"); seasonsList.add("Winter"); return seasonsList; } }