How to iterate list inside a lambda filter stream in Java 8?

Question

I have a Car class, each Car class has a list of Wheel class and each Wheel class has a integer field airPressure.

public class Car {
  private List<Wheel> wheels;
  public List<Wheel> getWheels() {
    return wheels;
  }
}

public class Wheel {
  private int airPressure;
  public int getAirPressure() {
    return airPressure;
  }
}

Now I have a list of Cars and I have to filter out all cars that have any wheels' air pressure larger than defaultValue. I'm filtering cars but I need to iterate through all wheels. Now I have code like this:

I have: List<Cars> cars, int defaultValue
List<Cars> filteredCars = cars.stream()
  .filter(car -> car.getWheels().get(0).getAirPressure() < defaultValue)
  .filter(car -> car.getWheels().get(1).getAirPressure() < defaultValue)
  .filter(car -> car.getWheels().get(2).getAirPressure() < defaultValue)
  ...

How to iterate wheels of each car when filtering cars?

Have a look at this howto page?

Jeroen Heier
– Jeroen Heier

2017-08-25 03:59:40 +00:00
Commented Aug 25, 2017 at 3:59 — Jeroen Heier
– Jeroen Heier, Commented Aug 25, 2017 at 3:59

shmosel · Accepted Answer · 2017-08-25 04:00:39Z

2

This will select only cars with all wheels' air pressure below defaultValue:

List<Car> filteredCars = cars.stream()
        .filter(car -> car.getWheels()
                .stream()
                .allMatch(wheel -> wheel.getAirPressure() < defaultValue))
        .collect(Collectors.toList());

answered Aug 25, 2017 at 4:00

shmosel

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2 Comments

cuegod Over a year ago

Thanks for your answer. Do you know what's the simplest way to find the max value of airPressure of all wheels of all cars?

shmosel Over a year ago

cars.stream().map(Car::getWheels).flatMap(List::stream).mapToInt(Wheel::getAirPressure).max()

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