public void writeExternal(ObjectOutput out) throws IOException {
        out.writeFloat(x);
        out.writeFloat(y);
    }
Writes the vector to an {@code ObjectOutput} object. The current instance
is unaffected.

<p>Used with serialization. Shouldn't be invoked directly by application
code.

@param out the object to write to (not null)
@throws IOException if the ObjectOuput cannot write a float
@see java.io.Externalizable
jme3-core/src/main/java/com/jme3/math/Vector2f.java