Question

I’m trying to find a way to extract a HashMap from a private static field within another class via Java.

eg.

Inside FooClass there is a static field that looks like this:

private Map entityRenderMap;

Then in its construct it has:

entityRenderMap = new HashMap();

How do you get the values within entityRenderMap via Reflection in Java? I’ve tried this but get errors:

cl = RenderManager.class.getDeclaredField("entityRenderMap");
        cl.setAccessible(true);
        Object foo = cl.get(this.entityRenderMap);
        Mod.log(cl.getName());

The error I get is:

java.lang.IllegalArgumentException: Can not set java.util.Map field RenderManager.entityRenderMap to java.util.HashMap
at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(Unknown Source)
at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(Unknown Source)
at sun.reflect.UnsafeFieldAccessorImpl.ensureObj(Unknown Source)
at sun.reflect.UnsafeObjectFieldAccessorImpl.get(Unknown Source

Answer 1

First, your code doesn’t match your explanation. Is it really a static field or is it not (your code says it’s not)?

If it is static, you should pass null as argument to cl.get() (you don’t need an instance to access static members).

However, I suspect that your field is actually not static, and your passing the wrong instance to cl.get(). The JavaDocs to Field.get() state it would throw an IllegalArgumentException in this case. You need to pass a RenderManager instance to this method. Your code looks like your passing a Map (the entityRenderMap).

And last, is this code inside your RenderManager class? I suspect this, because your accessing a field with this with the same name as the field you want to set. In this case, don’t use reflection at all!