@Override
    public boolean equals(final Object obj) {
        throw new UnsupportedOperationException(
                "com.yahoo.collections.Tuple2<T1, T2> does not support equals(Object) by design. Refer to JavaDoc for details.");
    }
equals(Object) will always throw UnsupportedOperationException. The
intention is always using the objects contained in the tuple directly.

@param obj
           ignored
@throws UnsupportedOperationException
            will always throw this when invoked
vespajlib/src/main/java/com/yahoo/collections/Tuple2.java