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Change private static final field using Java reflection

I have a class with a private static final field that, unfortunately, I need to change it at run-time.

Using reflection I get this error: java.lang.IllegalAccessException: Can not set static final boolean field

Is there any way to change the value?

Field hack = WarpTransform2D.class.getDeclaredField("USE_HACK");
hack.setAccessible(true);
hack.set(null, true);

Answer*

In openjdk17 I had to remove `final` modifier not just from `Field.modifiers`, but also from `Field.root.modifiers`.  
[`Field.root`](https://github.com/openjdk/jdk17u/blob/jdk-17%2B35/src/java.base/share/classes/java/lang/reflect/Field.java#L91) is used internally in `field.set(...)` [here](https://github.com/openjdk/jdk17u/blob/jdk-17%2B35/src/java.base/share/classes/java/lang/reflect/Field.java#L1124).  
So my code is this:
```java
    private static void makeStaticFinalFieldWritable( Field field ) {
      try {
        var lookup = MethodHandles.privateLookupIn( field.getClass(), MethodHandles.lookup() );
        var modifiersHandle = lookup.findVarHandle( field.getClass(), "modifiers", int.class );
        var modifiers = field.getModifiers();
        modifiersHandle.set( field, modifiers & ~Modifier.FINAL );

        var rootHandle = lookup.findVarHandle( field.getClass(), "root", Field.class );
        var root = ( Field ) rootHandle.get( field );
        if ( root != null && root != field ) {
          makeStaticFinalFieldWritable( root );
        }
      }
      catch ( IllegalAccessException | NoSuchFieldException e ) {
        throw new Error( e );
      }
    }
```

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– Community Bot

2024-04-17 20:50:55 +00:00
Commented Apr 17, 2024 at 20:50

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Change private static final field using Java reflection

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