Java – what is the best way to navigate complex trees of different objects?

For example:

class Vehicle {
    Collection<Axle> axles;
}

class Axle {
    Collection<Wheel> wheels;
}

class Wheel {
    // I think there are dually rims that take two tires -- just go with it
    Collection<Tire> tires;
}

class Tire {
    int width;
    int diameter;
}

I have a service through which I can get a collection of all vehicle objects I know Now that I have a tire of a specific width and diameter, I want to find a vehicle that can accept it The simple approach is to have a set of four nested loops, as follows:

for (Vehicle vehicle : vehicles) {
    for (Axle axle : vehicle.getAxles()) {
        for (Wheel wheel : axle.getWheels()) {
            for (Tire tire : wheel.getTires()) {
                if (tire.width == targetWidth
                 && tire.diameter == targetDiameter) {
                    // do something
                    break;
                }
            }
        }
    }
}

Is there a good design pattern? Or do you want to use a better data structure? Would it be better to keep an index in the location mapped to the tire information of the vehicle?

Editor: answer questions in comments

yes

yes

Not special

Sometimes it's just a vehicle, sometimes it's just an axle – two different environments

Yes, when I need the shaft

Edit2: further expand metaphor to explain the above two situations:

Background 1 – I want to know the vehicle, so I can send a worker to collect the vehicle and bring it back

Background 2 – I want to know the axles and tires because I'm trying to do this for the vehicle

Solution

You can use Java 8 streams to flatten loops

vehicles.stream()
    .flatMap(vehicle -> vehicle.getAxles().stream())
    .flatMap(axle -> axle.getWheels().stream())
    .flatMap(wheel -> wheel.getTires().stream())
    .filter(tire -> tire.width == targetWidth
             && tire.diameter == targetDiameter)
    .forEach(tire -> {
        // do something
    });

The advantage of streaming is that you can insert additional filters, filters, findany, etc. anywhere in the sequence