example code

        val busIdsOnTheRouteStart = IntStream.range(0, 15);
        val busIdsOnTheRouteEnd = IntStream.range(16, 30);

        val busIdsInboundToggleTuples = busIdsOnTheRouteStart.boxed()
                .collect(toMap(identity(), id -> Toggle.from(Direction.INBOUND, Direction.OUTBOUD)));
        val busIdsOutboundToggleTuples = busIdsOnTheRouteStart.boxed()
                .collect(toMap(identity(), id -> Toggle.from(Direction.OUTBOUD, Direction.INBOUND)));

        val busIdDirectionToggleTuples = new HashMap<Integer, Toggle<Direction>>();
        busIdDirectionToggleTuples.putAll(busIdsInboundToggleTuples);
        busIdDirectionToggleTuples.putAll(busIdsOutboundToggleTuples);


        val generatedTrips = new ArrayList<Trip>();
        busIdDirectionToggleTuples.forEach((busId, directionToggle) -> {
            generatedTrips.add(genTrip(busId, directionToggle.get(), ...));
            directionToggle.toggle();
        });

Toggle.java

import java.util.ArrayList;
import java.util.HashMap;
import java.util.stream.IntStream;

import lombok.EqualsAndHashCode;
import lombok.ToString;
import lombok.val;

import static java.util.function.Function.identity;
import static java.util.stream.Collectors.toMap;
import static org.apache.commons.lang3.Validate.notNull;

@ToString
@EqualsAndHashCode
public class Toggle<T> {

    private final T baseValue;
    private final T toggledValue;

    private T currentValue;

    public Toggle(T baseValue, T toggledValue) {
        this.baseValue = notNull(baseValue);
        this.toggledValue = notNull(toggledValue);

        this.currentValue = baseValue;
    }

    public static <T> Toggle<T> from(T baseValue, T toggledValue) {
        return new Toggle<>(baseValue, toggledValue);
    }


    public T get() {
        return currentValue;
    }

    public T getAndToggle() {
        val currVal = get();

        toggle();
        return currVal;
    }

    public T toggleAndGet() {
        toggle();
        return get();
    }

    public void toggle() {
        currentValue = (currentValue == baseValue) ? toggledValue : baseValue;
    }
}