浅谈Arrays.asList() 和ArrayList类型区别

时间:2021-08-11 07:11:00

<pre name="code" class="html"><pre name="code" class="html">Arrays.asList()

将一个数组转化为一个List对象,这个方法会返回一个ArrayList类型的对象, 这个ArrayList类并非java.util.ArrayList类,而是Arrays类的静态内部类!用这个对象对列表进行添加删除更新操作,就会报UnsupportedOperationException异常。

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<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);

输出结果:

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<pre name="code" class="html">arraylist:true==[yz_b_insert, yz_b_del, yz_b_update, yz_b_see]
<pre name="code" class="html">arrays.asList():false@@@@@[yz_b_insert,yz_b_del,yz_b_update,yz_b_see]

要是用<pre name="code" class="html">contains 来判断集合中存在某个字符串,注意 <pre name="code" class="html">arraylist转化的不可用 

本人测试不可以,有高人可以指点一下 

下面是网上找的资源 

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<span style="color: rgb(102, 102, 102); font-family: Tahoma;">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。 </span><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><span style="color: rgb(102, 102, 102); font-family: Tahoma;">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? </span><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><span style="color: rgb(102, 102, 102); font-family: Tahoma;">我们可以写一个类似的方法,里面直接采用java.util.ArrayList即可。 </span><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><span style="color: rgb(102, 102, 102); font-family: Tahoma;">比如: </span><br style="color: rgb(102, 102, 102); font-family: Tahoma;" /><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;
    }
}

测试代码如下:

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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;
    }
}

输出结果:

[Larry, Moe, Curly]
[[Spring, Summer, Autumn, Winter]]
[Larry, Moe, Curly, Hello]

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