用于匿名内部类的泛型

匿名内部类

泛型还可以使用于内部类和匿名内部类。

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都通过使用匿名内部类实现了Generator接口，并且他们都只有private的构造器，这就意味着要想创建这两个类的对象，必须使用generator方法。其中，Customer类的generator()方法每次调用都会返回一个新的Generator<Customer>对象，但我们其实并不需要多个Generator对象。这时，就可以像Teller类一样，只创建一个public的generator对象。在main方法中，这两种创建Generator对象的方法在fill()中都用到了。

由于Customer中的generator()方法，以及Teller中的Generator对象都声明成static，所以它们都无法作为接口的一部分，因此不能用接口这种特定的惯用法来泛化这两者。尽管如此，它们在fill()方法中都工作得很好。（//TODO 看不懂）