Java集合(2)：两个生成器的例子：Collection生成器CollectionData及Map生成器MapData

Collection生成器CollectionData

CollectionData体现了适配器模式的设计思想，它能把实现Generator接口的类的对象(包括上一章数组中的各种RandomGenerator)都复制到自身当中。

import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.Set;

interface Generator<T> {
    T next();
}

class CollectionData<T> extends ArrayList<T> {
    private static final long serialVersionUID = 1L;
    public CollectionData(Generator<T> gen, int quantity) {
        for (int i = 0; i < quantity; i++)
            add(gen.next());
    }
    public static <T> CollectionData<T> list(Generator<T> gen, int quantity) {
        return new CollectionData<T>(gen, quantity);
    }
}

class Animal implements Generator<String> {
    private String[] items = { "Dog", "Pig", "Cat" };
    private int index;
    @Override
    public String next() {
        return items[index++];
    }
}

public class Test2 {
    public static void main(String[] args) {
        Set<String> set = new LinkedHashSet<String>(new CollectionData<String>(new Animal(), 3));
        System.out.println(set); // [Dog, Pig, Cat]
        set.addAll(CollectionData.list(new Animal(), 3));
        System.out.println(set); // [Dog, Pig, Cat]
    }
}

Map生成器MapData

我们可以使用同样的方式生成Map，我们可以Generator<K>，Generator<V>分开生成，也可以使用Pair<K, V>组装好K,V再生成。

import java.util.Iterator;

import java.util.LinkedHashMap;

class Pair<K, V> {
    public final K key;
    public final V value;

    public Pair(K k, V v) {
        this.key = k;
        this.value = v;
    }
}

class MapData<K, V> extends LinkedHashMap<K, V> {
    private static final long serialVersionUID = 1L;

    // A single Pair Generator:
    public MapData(Generator<Pair<K, V>> gen, int quantity) {
        for (int i = 0; i < quantity; i++) {
            Pair<K, V> p = gen.next();
            put(p.key, p.value);
        }
    }

    public static <K, V> MapData<K, V> map(Generator<Pair<K, V>> gen, int quantity) {
        return new MapData<K, V>(gen, quantity);
    }

    // Two separate Generators:
    public MapData(Generator<K> genK, Generator<V> genV, int quantity) {
        for (int i = 0; i < quantity; i++) {
            put(genK.next(), genV.next());
        }
    }

    public static <K, V> MapData<K, V> map(Generator<K> genK, Generator<V> genV, int quantity) {
        return new MapData<K, V>(genK, genV, quantity);
    }

    // A key Generator and a single value:
    public MapData(Generator<K> genK, V value, int quantity) {
        for (int i = 0; i < quantity; i++) {
            put(genK.next(), value);
        }
    }

    public static <K, V> MapData<K, V> map(Generator<K> genK, V value, int quantity) {
        return new MapData<K, V>(genK, value, quantity);
    }

    // An Iterable and a single value:
    public MapData(Iterable<K> genK, V value) {
        for (K key : genK) {
            put(key, value);
        }
    }

    public static <K, V> MapData<K, V> map(Iterable<K> genK, V value) {
        return new MapData<K, V>(genK, value);
    }
}

class Letters implements Generator<Pair<Integer, String>>, Iterable<Integer> {
    private int size = 9;
    private int number = 1;
    private char letter = 'A';

    @Override
    public Pair<Integer, String> next() {
        return new Pair<Integer, String>(number++, "" + letter++);
    }

    @Override
    public Iterator<Integer> iterator() {
        return new Iterator<Integer>() {
            @Override
            public Integer next() {
                return number++;
            }

            @Override
            public boolean hasNext() {
                return number < size;
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }
}

public class Test3 {
    public static void main(String[] args) {
        // A single Pair Generator test
        MapData<Integer, String> data1 = MapData.map(new Letters(), 11);
        System.out.println(data1); // {1=A, 2=B, 3=C, 4=D, 5=E, 6=F, 7=G, 8=H, 9=I, 10=J, 11=K}
        // An Iterable and a single value test
        MapData<Integer, String> data2 = MapData.map(new Letters(), "Pop");
        System.out.println(data2); // {1=Pop, 2=Pop, 3=Pop, 4=Pop, 5=Pop, 6=Pop, 7=Pop, 8=Pop}
    }
}