public JoinOperator swapEquivalent() {
        switch (this) {
            case EQUAL:
                return EQUAL;
            case NOT_EQUAL:
                return NOT_EQUAL;
            case LESS_THAN:
                return GREATER_THAN;
            case LESS_OR_EQUAL:
                return GREATER_OR_EQUAL;
            case GREATER_THAN:
                return LESS_THAN;
            case GREATER_OR_EQUAL:
                return LESS_OR_EQUAL;
        }
        throw new IllegalStateException(
            "There is no swap-equivalent " + JoinOperator.class.getSimpleName() + " to " + this
        );
    }
Returns a JoinOperator that would produce an equivalent predicate when
the arguments to the operator are applied swapped.

@return a JoinOperator that would produce an equivalent predicate when
the arguments to the operator are applied swapped.
@throws IllegalStateException if no such equivalent JoinOperator exists
runtime-parent/runtime-join/src/main/java/com/speedment/runtime/join/stage/JoinOperator.java