Using Java 8, Forge 1.12.2
I've been trying to use reflection to change a private variable in another class, I'm able to get the class, and the variable,

*I've tried to use the public set method to change the variable, that doesn't work, and ends in this error:

java.lang.IllegalArgumentException: object is not an instance of declaring class

*I've tried changing the variable to accesible = true and then changing it, resulting in this error:

java.lang.IllegalArgumentException: Can not set int field playerProperties.VanillaSpellsCapability.mirrorspellSpread to java.lang.Class

 

The Code:

Class clad = Class.forName(message.cladName);
                
                Field MSS = clad.getDeclaredField(message.mirrorspellSpread);
                
                MSS.setAccessible(true);

                MSS.set(clad, 1);
                //Method SetMS = clad.getMethod("setIsMSSpreadOut", Integer.TYPE);
                //SetMS.invoke(clad, 1);

Edited December 17, 20186 yr by CorruptedVulture

Terribly sorry, wrong forum.

 

8 minutes ago, CorruptedVulture said:

*I've tried to use the public set method to change the variable, that doesn't work, and ends in this error:

java.lang.IllegalArgumentException: object is not an instance of declaring class

If the method is public then you don't need reflection. Anyway, as the error clearly states you are passing an object as an instance of the class while the object in question isn't an instance of said class. This is one of reflection's basics.

 

9 minutes ago, CorruptedVulture said:

java.lang.IllegalArgumentException: Can not set int field playerProperties.VanillaSpellsCapability.mirrorspellSpread to java.lang.Class

Same here - you are passing a Class as the instance, which will never be the case. 

 

https://www.oracle.com/technetwork/articles/java/javareflection-1536171.html

 

Ok, I tried with the new instance by declaring a new object, and setting it to be the class's new instance, and my intentions with this was to update a capability variable on the client-side, however it's just as I thought that making a new instance wouldn't affect the player's capability.
So is there any other solution? Like to use the class instance I already have instead of declaring a new one?

The new Code:
 

Class clad = Class.forName(message.cladName);
                Object cc = clad.newInstance();
                //Field MSS = clad.getDeclaredField(message.mirrorspellSpread);
                /*
                MSS.setAccessible(true);

                MSS.set(clad, 1);*/

                Method SetMS = clad.getMethod("setIsMSSpreadOut", Integer.TYPE);
                SetMS.invoke(cc, 1);

4 minutes ago, CorruptedVulture said:

So is there any other solution? Like to use the class instance I already have instead of declaring a new one?

Well, yes, you need to use the instance you want to update the value of. 

Except I can't do that because using the instance I want to change results in this error
java.lang.IllegalArgumentException: object is not an instance of declaring class
Using this code
//Method SetMS = clad.getMethod("setIsMSSpreadOut", Integer.TYPE);
//SetMS.invoke(clad, 1);

Keep in mind, not declaring a new object, like here
 Object cc = clad.newInstance();

So then is there anything else I can do, to use the instance I got?

Edited December 17, 20186 yr by CorruptedVulture

15 minutes ago, CorruptedVulture said:

//SetMS.invoke(clad, 1);

Class != Instance of said class.

Well that definitely sheds alot of light on the situation, thanks.