Java中关于数组转换成List的注意事项

问题代码

package org.emacsist;

import java.util.Arrays;
import java.util.List;

/**
 * Created by sky on 16-2-14.
 */
public class TestHello {
    public static void main(String[] args) {
        List<String> arg = Arrays.asList(args);
        arg.add("出现问题了.");
        System.out.println(arg);
    }
}

一运行，就报如下错误

Exception in thread "main" java.lang.UnsupportedOperationException
	at java.util.AbstractList.add(AbstractList.java:148)
	at java.util.AbstractList.add(AbstractList.java:108)
	at org.emacsist.TestHello.main(TestHello.java:12)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

Process finished with exit code 1

原因

Arrays.asList(args);

这个方法，根据JavaDoc

它返回的是一个固定大小的List，这意味着不支持任何修改的操作。比如add, remove等.

返回一个可修改的List

package org.emacsist;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * Created by sky on 16-2-14.
 */
public class TestHello {
    public static void main(String[] args) {
        List<String> arg = new ArrayList<>(Arrays.asList(args));
        arg.add("不会出现问题了.");
        System.out.println(arg);
    }
}

执行的结果如下:

[不会出现问题了.]

Process finished with exit code 0