版权声明:如笔记。一点一滴,伴我成长。可转载 https://blog.csdn.net/Butterfly_resting/article/details/89402913
java.lang.IllegalArgumentException: Can not set final [B field java.lang.String.value to java.lang.String
at java.base/jdk.internal.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167)
at java.base/jdk.internal.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171)
at java.base/jdk.internal.reflect.UnsafeQualifiedObjectFieldAccessorImpl.set(UnsafeQualifiedObjectFieldAccessorImpl.java:83)
at java.base/java.lang.reflect.Field.set(Field.java:780)
at string.StringDemo.main(StringDemo.java:18)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at com.intellij.rt.execution.application.AppMainV2.main(AppMainV2.java:131)
简述:在通过反射修改String 的final字段的时候,出现该IllegalArgumentException异常。代码如下:
String str = "123456";
try {
Field value = String.class.getDeclaredField("value");// 返回一个 Field 对象
value.setAccessible(true);//不设置将从抛出IllegalAccessException,因为String的value是final
value.set(str,"123");
System.out.println(str);
} catch (Exception e) {
e.printStackTrace();
}
IllegalArgumentException
- 如果指定对象不是声明底层字段(或者其子类或实现者)的类或接口的实例,或者解包转换失败。因为JVM在编译时期, 就把final类型的String进行了优化, 在编译时期就会把String处理成常量。所以无法修改类似String str = "123456"的值。
官方文档也说明指定对象是声明底层字段(或者其子类或实现者)的类或接口的实例才能修改String的值。
实例如下:
import java.lang.reflect.Field;
class People{
String str = "123";
}
public class StringDemo {
public static void main(String[] args) {
People p = new People();
System.err.println(p.str);//123
try {
Field field = People.class.getDeclaredField("str");
field.setAccessible(true);
field.set(p,"0");
System.err.println(p.str);//0 修改String值成功
} catch (Exception e) {
e.printStackTrace();
}
}
}