I have a class Vehicule and 3 subclasses Voiture, Camion and Moto. I also have a method getVehicules for the all vehicules (i.e. camion, voiture, moto) but I want to print a specific type like Voiture.

I don't know how to solve it .

 List<Vehicule> vehicules = new ArrayList<>();

    public void getVehicules() {
            vehicules.forEach(vehicule->{
                System.out.println(vehicule);
            });     

     }
    
    public void getVoitures() {
        Iterator iterator = vehicules.iterator();
        while(iterator.hasNext()) {

      //I want to do a condtion if vehicule is voiture it will disaplay

            if(vehicules.equals(voiture)) {
                System.out.println(iterator);
            }
        }
    }

CodePudding user response：

Check this out, instanceof would help here :-

class Vehicule {

}

class Voiture extends Vehicule {

    @Override
    public String toString() {
        return "Voiture";
    }
}

class Camion extends Vehicule {

    @Override
    public String toString() {
        return "Camion";
    }
}

class Moto extends Vehicule {
    @Override
    public String toString() {
        return "Moto";
    }
}

public class Operation {
    
    static List<Vehicule> vehicules = new ArrayList<>();
    
    public static void main(String[] args) {
        vehicules.add(new Camion());
        vehicules.add(new Moto());
        vehicules.add(new Voiture());
        //Prints all objects
        getVehicules();
        //Prints only voiture
        getVoitures();

    }

    public static void getVehicules() {
        vehicules.forEach(vehicule -> {
            System.out.println(vehicule);
        });

    }

    public static void getVoitures() {
        Iterator iterator = vehicules.iterator();
        while (iterator.hasNext()) {
            Object vehicule = iterator.next();
            if (vehicule instanceof Voiture) {
                System.out.println(vehicule);
            }
        }
    }


}

CodePudding user response：

How to compare two data type in Java You can get the type (a java.lang.Class) of an object using object.getClass().

You can compare two classes using equals(...); e.g.

if (obj1.getClass().equals(obj2.getClass())

You can test if an object has a specific class in a couple of ways

if (obj.getClass().equals(Car.class))

if (obj instanceof Car)

(They do slightly different things. The latter tests if obj is a Car or a subclass of Car and will return false if obj is null.)

There are methods on the Class class that will give the classes simple name or its full name ... or you can just use the Class.toString() method.

Just for the record, another way to solve the problem that doesn't involve using the class names would be to define a second (abstract) method in the superclass that returns a String that denotes the kind of the vehicle; e.g.

   public abstract class Vehicle {
      ...
      public abstract String getType();
   }

   public class Car extends Vehicle {
      
      @Override
      public String getType() {
          return "Car";
      }
   }

CodePudding user response：

`switch` expressions

In Java 14 , use switch expressions.

Some untested code:

switch ( véhicule.getClass() ) {
    case Voiture.class  -> System.out.println( … );
    case Camion.class   -> System.out.println( … );
    case Moto.class     -> System.out.println( … );
}

Wrap that in a for-each loop.

for( Véhicule véhicule: véhicules)
{
    …
}

switch expressions

`switch` expressions