public String getAssetName() {
        return key != null ? key.getName() : null;
    }
Returns the asset key name of the asset from which this material was loaded.
<p>This value will be null unless this material was loaded from a .j3m file.</p>

@return Asset key name of the .j3m file, or null if not loaded from a file.
jme3-core/src/main/java/com/jme3/material/Material.java