java.lang.UnsupportedOperationException解决方法
在项目中对List进行操作时报错java.lang.UnsupportedOperationException,后来发现操作的List是由数组转换而成的,通过看源码发现问题,并写测试程序如下。
代码块:
public class ListTest { public static void main(String[] args) { String[] array = {"1","2","3","4","5"}; List<String> list = Arrays.asList(array); list.add("6"); } }
执行结果:
Exception in thread "main" java.lang.UnsupportedOperationException at java.util.AbstractList.add(AbstractList.java:148) at java.util.AbstractList.add(AbstractList.java:108) at com.atguigu.test.ListTest.main(ListTest.java:11) 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:498) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
发生问题的原因如下:
调用Arrays.asList()产生的List中add、remove方法时报异常,这是由于Arrays.asList()返回的是Arrays的内部类ArrayList, 而不是java.util.ArrayList。Arrays的内部类ArrayList和java.util.ArrayList都是继承AbstractList,remove、add等方法在AbstractList中是默认throw UnsupportedOperationException而且不作任何操作。java.util.ArrayList重写这些方法而Arrays的内部类ArrayList没有重写,所以会抛出异常。解决方法如下:
public class ListTest { public static void main(String[] args) { String[] array = {"1","2","3","4","5"}; List<String> list = Arrays.asList(array); List arrList = new ArrayList(list); arrList.add("6"); } }