匿名內(nèi)部類

泛型還可以使用于內(nèi)部類和匿名內(nèi)部類。

class Customer {
    private static long counter = 1;
    private final long id = counter++;

    private Customer() {

    }

    public String toString() {
        return "Customer " + id;
    }

    public static Generator<Customer> generator() {
        return new Generator<Customer>() {
            @Override
            public Customer next() {
                return new Customer();
            }
        };
    }
}

class Teller {
    private static long counter = 1;
    private final long id = counter++;

    private Teller() {
    }

    public String toString() {
        return "Teller " + id;
    }

    public static Generator<Teller> generator = new Generator<Teller>() {
        @Override
        public Teller next() {
            return new Teller();
        }
    };
}


public class BankTeller {
    public static void serve(Teller t, Customer c) {
        System.out.println(t + " serves " + c);
    }

    public static void main(String[] args) {
        Random rand = new Random(47);
        Queue<Customer> line = new LinkedList<>();
        Generators.fill(line, Customer.generator(), 15);
        List<Teller> tellers = new ArrayList<>();
        Generators.fill(tellers, Teller.generator, 4);
        for (Customer c : line) {
            serve(tellers.get(rand.nextInt(tellers.size())), c);
        }
    }
}

// Outputs
Teller 3 serves Customer 1
Teller 2 serves Customer 2
Teller 3 serves Customer 3
Teller 1 serves Customer 4
Teller 1 serves Customer 5
Teller 3 serves Customer 6
Teller 1 serves Customer 7
Teller 2 serves Customer 8
Teller 3 serves Customer 9
Teller 3 serves Customer 10
Teller 2 serves Customer 11
Teller 4 serves Customer 12
Teller 2 serves Customer 13
Teller 1 serves Customer 14
Teller 1 serves Customer 15

上面的Customer和Teller都通過使用匿名內(nèi)部類實(shí)現(xiàn)了Generator接口，并且他們都只有private的構(gòu)造器，這就意味著要想創(chuàng)建這兩個(gè)類的對(duì)象，必須使用generator方法。其中，Customer類的generator()方法每次調(diào)用都會(huì)返回一個(gè)新的Generator<Customer>對(duì)象，但我們其實(shí)并不需要多個(gè)Generator對(duì)象。這時(shí)，就可以像Teller類一樣，只創(chuàng)建一個(gè)public的generator對(duì)象。在main方法中，這兩種創(chuàng)建Generator對(duì)象的方法在fill()中都用到了。

由于Customer中的generator()方法，以及Teller中的Generator對(duì)象都聲明成static，所以它們都無法作為接口的一部分，因此不能用接口這種特定的慣用法來泛化這兩者。盡管如此，它們?cè)?code>fill()方法中都工作得很好。（//TODO 看不懂）