使用反射修改final属性

情型1：static final属性，无法修改其值。

package m5.d7;  

import java.lang.reflect.Field;  

public class FieldTest {
    public static void main(String[] args) {
        try {
            A a = new A();  

            Field field = a.getClass().getDeclaredField("a");  

            field.setAccessible(true);  

            field.set(a, 2);  

            System.out.println(field.get(a));
        } catch (SecurityException e) {
            e.printStackTrace();
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
    }
}  

class A {
    private static final int a = 1;
}

运行

java.lang.IllegalAccessException: Can not set static final int field m5.d7.A.a to java.lang.Integer
    at sun.reflect.UnsafeFieldAccessorImpl.throwFinalFieldIllegalAccessException(Unknown Source)
    at sun.reflect.UnsafeFieldAccessorImpl.throwFinalFieldIllegalAccessException(Unknown Source)
    at sun.reflect.UnsafeQualifiedStaticIntegerFieldAccessorImpl.set(Unknown Source)
    at java.lang.reflect.Field.set(Unknown Source)
    at m5.d7.FieldTest.main(FieldTest.java:16)

情型2：final属性，可以修改其值。

package m5.d7;  

import java.lang.reflect.Field;  

public class FieldTest {
    public static void main(String[] args) {
        try {
            A a = new A();  

            Field field = a.getClass().getDeclaredField("a");  

            field.setAccessible(true);  

            field.set(a, 2);  

            System.out.println(field.get(a));
        } catch (SecurityException e) {
            e.printStackTrace();
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
    }
}  

class A {
    private final int a = 1;
}

运行

2