How to loop through an array of different objects in Java using the enhanced for loop-CodePudding

I have an array of objects of classes Car, Bicycle, and Van. I want to iterate through all objects and execute the go() method. go() for one class looks like this.

public class Van extends Vehicle {
    @Override
    public void go() {
        System.out.println("Van started");
    }
}

Each of these classes inherits the Vehicle class. So, when I initialized an array of type Vehicle[], it worked without a problem.

Now I want to do the same with an array of Object[]. But as the objects are of different types, I get an error asking to cast the x to the relevant datatype (in this case Car, Van, or Bicycle). I tried using the x.getClass() but it gives me answers as class Car, class Bicycle, etc. When I try to execute go() method, I get an error saying The method go() is undefined for the type Class<capture#3-of ? extends Object>


public class App {
    public static void main(String[] args) throws Exception {
        Car car = new Car();
        Bicycle bicycle = new Bicycle();
        Van van = new Van();

        Object[] racers = {car, bicycle, van};  

        for(Object x : racers) {
            System.out.println(x.getClass()); 

            x.getClass().go();  // error - The method go() is undefined for the type Class<capture#3-of ? extends Object>
        }
    }
}

CodePudding user response：

Found the answer

public class App {
    public static void main(String[] args) throws Exception {
        Car car = new Car();
        Bicycle bicycle = new Bicycle();
        Van van = new Van();

        Object[] racers = {car, bicycle, van};  

        for(Object x : racers) {
            System.out.println(x.getClass()); 

            ((Vehicle) x).go();  // this is the only change I made
        }
    }
}

CodePudding user response：

The following would have worked

    Vehicle[] racers = {car, bicycle, van};  
    for (Vehicle x : racers) { ... x.go();

Dynamic detection does works too. You could use the modern Stream<?>.

    Object[] racers = {car, bicycle, van};  

    Arrays.stream(racers)
       .filter(r -> r instanceOf(Vehicle)
       .map(Vehicle.class::cast)
       .forEach(r -> {
            r.go(); ...
       };

CodePudding user response：

You have to use the "instanceof" keyword

    Object o = "testString";

    if (o instanceof Integer) {
        System.out.println("is Integer");
        return
    }

    if (o instanceof String) {
        System.out.println("is String");
        return;
    }