How can I change the generic type in child-classes in Java

Question

How can I change the generic type in child-classes. I know, that i can override method load(); But i want to make the universal method for all children. I have abstract super class

public abstract class Vehicle <T extends Human> {
    T t;
    private final int maxPassengers;
    private Set<T> currentPassengers = new HashSet<>();

    public Vehicle(int maxPassengers) {
       this.maxPassengers = maxPassengers;
    }

    public void load (T human) throws ToManyPassangersExeption {
        if (currentPassengers.size()<maxPassengers)
            currentPassengers.add(human);
        else
            throw new ToManyPassangersExeption();
    }
}

load() realize loading Human to vehicle. I have different types of Human. For example:

public class Policeman extends Human {
    }

In my class PoliceCar, i what to load only Policemen.

public class PoliceCar <T extends Policeman> extends Vehicle {
    T t;

    public PoliceCar() {
        super(5);
    }
}

Using this code, i can load all instanceof Human to PoliceCar.

How can i load only Policeman in PoliceCar without Overriding method load()?

score 2 · Accepted Answer · edited May 23 '17 at 11:54

2

Declare the PoliceCar type with a non-raw superclass:

class PoliceCar<T extends Policeman> extends Vehicle<T>

Then the load method will require a T parameter, where T is a subclass of Policeman.

See What is a raw type and why shouldn't we use it?.

edited May 23 '17 at 11:54

Community

1
1

answered Apr 06 '17 at 20:02

Andy Turner

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Just `PoliceCar extends Vehicle` may be good enougth too. – Zefick Apr 06 '17 at 20:06
@Zefick indeed. But the critical bit is adding the type parameter to `Vehicle`. – Andy Turner Apr 06 '17 at 20:07
Thank you guys! Now its Work! – A. Kashnikov Apr 06 '17 at 20:08

How can I change the generic type in child-classes in Java

1 Answers1