Dynamically change private static final fields in Java

Overview

In Java, a method of setAccessible (true) using reflection is widely known as a means of changing the value of a private field that is normally inaccessible from the outside.

We will show you how to apply this method to dynamically change the final field.

Sample code

Main.java

public class Main {

    public static void main(String[] args) throws Exception {

        TargetClass clazz = new TargetClass();
        System.out.println("Before update: " + clazz.getTargetField());                    // Before update: 1

        Field targetField = clazz.getClass().getDeclaredField("TARGET_FIELD");     //Get the Field object for the access to be updated.
        Field modifiersField = Field.class.getDeclaredField("modifiers");          //Since the Field class uses modifiers to determine the access of the field to be accessed, update this.
        modifiersField.setAccessible(true);                                        //The modifiers themselves are private, so make them accessible.
        modifiersField.setInt(targetField,
                targetField.getModifiers() & ~Modifier.PRIVATE & ~Modifier.FINAL); //Remove private and final from the modifiers of the Field object for update target access.
        targetField.set(null, 1000);                                               //Value update: 1 -> 1000

        System.out.println("_People People People People_");                                  // _People People People People_
        System.out.println("After update: ＞　 " + clazz.getTargetField() + " 　＜");       // After update: ＞　 1000 　＜
        System.out.println("       ￣Y^Y^Y^Y￣");                                     //       ￣Y^Y^Y^Y￣

    }
}

TargetClass.java

public class TargetClass {

    private static final Integer TARGET_FIELD = 1;

    public Integer getTargetField() {
        return TARGET_FIELD;
    }

}

Supplement

In an environment where SecurityManager is enabled, private static final fields cannot be changed dynamically using the above method. Also, if you are inlined by compile-time optimization, you cannot change the value using the above method. (In this case, no error will occur.)

reference

http://stackoverflow.com/questions/3301635/change-private-static-final-field-using-java-reflection