泛型也可以用于接口，例如生成器，这是一种专门负责创意对象的类。实际上是工厂方法设计模式的一种应用。不同的是它不需要任何参数。
一般一个生成器只定义一个方法，该方法用于产生新的 对象。
例子：
public interface Generator<T> { T next(); }
辅助类：
public class Coffee {
private static long counter = 0;
private final long id = counter++;
public String toString() {
return getClass().getSimpleName() + " " + id;
}
}
public class Latte extends Coffee {}
public class Mocha extends Coffee {}
public class Americano extends Coffee {}
实现Generator<Coffer>接口，它能够随机生产不同类型的Offee对象
public class CoffeeGenerator
implements Generator<Coffee>, Iterable<Coffee> {
private Class[] types = { Latte.class, Mocha.class,
Cappuccino.class, Americano.class, Breve.class, };
private static Random rand = new Random(47);
public CoffeeGenerator() {}
// For iteration:
private int size = 0;
public CoffeeGenerator(int sz) { size = sz; }
public Coffee next() {
try {
return (Coffee)
types[rand.nextInt(types.length)].newInstance();
// Report programmer errors at run time:
} catch(Exception e) {
throw new RuntimeException(e);
}
}
class CoffeeIterator implements Iterator<Coffee> {
int count = size;
public boolean hasNext() { return count > 0; }
public Coffee next() {
count--;
return CoffeeGenerator.this.next();
}
public void remove() { // Not implemented
throw new UnsupportedOperationException();
}
};
public Iterator<Coffee> iterator() {
return new CoffeeIterator();
}
public static void main(String[] args) {
CoffeeGenerator gen = new CoffeeGenerator();
for(int i = 0; i < 5; i++)
System.out.println(gen.next());
for(Coffee c : new CoffeeGenerator(5))
System.out.println(c);
}
}
参数化的Generator接口确保next()方法的返回值是参数的类型，
