public void readExternal(ObjectInput in) throws IOException {
        x = in.readFloat();
        y = in.readFloat();
        z = in.readFloat();
        w = in.readFloat();
    }
Sets the quaternion from an {@code ObjectInput} object.

<p>Used with serialization. Should not be invoked directly by application
code.

@param in the object to read from (not null)
@throws IOException if the ObjectInput cannot read a float
@see java.io.Externalizable
jme3-core/src/main/java/com/jme3/math/Quaternion.java