Writing a for-each loop to get objects from an ArrayList [closed]

问题

I want to write a for loop using the for-each syntax:

for(Obj o : ArrayList<Obj>)

As in this example:

class Car{
    int number;
    public Car(int num){ number = num; }
    int getNumber(){ return this.number; }
}

class CarPark{
    ArrayList<Car> cars;
    public CarPark(){ cars = new ArrayList<Car>(); }
}

public class Main{
    public static void main(String[] args){
        CarPark p = new CarPark();
        p.add(new Car(123));
        p.add(new Car(456));
        p.add(new Car(789));

        for(Car c : p.cars){
            System.out.println(c.getNumber());
        }
    }
}

How do I write the loop? Is this syntax possible?

回答1:

Your for-each loop has no problem.

There is just one point you must modify. To adding new Car objects to ArrayList, use p.cars.add().

public static void main(String[] args) {
    CarPark p = new CarPark();
    p.cars.add(new Car(123));
    p.cars.add(new Car(456));
    p.cars.add(new Car(789));

    for (Car c : p.cars) {
        System.out.println(c.getNumber());
    }
}

So the ArrayList cars is a member of CarPark class object p, that you can access it through p.cars.

回答2:

Yes. You can do that. Apart from the naming convention, everything seems to be fine.

Now you are iterating using foreach loop.

if (p.getCars() != null) {
    for (Car car : p.getCars()) {
        System.out.println(car.getCarNumber());
    }
}

If you are looking for a traditional for loop:

for (int i = 0; i < p.size(); i++) {
    System.out.println(p.get(i).getNumber()); 
}

The foreach loop is usually preferable to the traditional style.

回答3:

With Java 8 you can use a simple lambda expression:

p.cars.forEach(c -> System.out.println(c.getNumber()));

This is equivalent to your for-loop.

来源：https://stackoverflow.com/questions/32550645/writing-a-for-each-loop-to-get-objects-from-an-arraylist

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