@Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final OgreMaterialKey other = (OgreMaterialKey) obj;
        if (!super.equals(other)) {
            return false;
        }
        if (this.matExts != other.matExts && (this.matExts == null || !this.matExts.equals(other.matExts))) {
            return false;
        }
        return true;
    }
<code>OgreMaterialKey</code> allows specifying material extensions, which map
from Ogre3D base materials to jME3 materials
jme3-plugins/src/ogre/java/com/jme3/scene/plugins/ogre/matext/OgreMaterialKey.java