迭代器模式

创建一个Aggregate<E>接口，表示待遍历数据集：

/*待遍历的数据集*/
public interface Aggregate<E> {
    /*添加*/
    void addEle(E element);
    /*移除*/
    void removeEle(E element);
    /*获取迭代器*/
    CustomIterator<E> createCustomIterator();
}

创建一个Aggregate<E>接口的实现类ConcreteArrayAggregate<E>：

/*待遍历的数据集类型为：数组类型*/
public class ConcreteArrayAggregate<E> implements Aggregate<E> {
    private E[] array = (E[]) new Object[0];
    @Override
    public void addEle(E element) {
        array = ArrayUtil.append(array, element);
    }
    @Override
    public void removeEle(E element) {
        array = ArrayUtil.removeEle(array, element);
    }
    @Override
    public CustomIterator<E> createCustomIterator() {
        return new ConcreteArrayCustomIterator<E>(array);
    }
}

创建一个Aggregate<E>接口的实现类ConcreteListAggregate<E>：

/*待遍历的数据集类型为：列表类型*/
public class ConcreteListAggregate<E> implements Aggregate<E> {
    private List<E> list = new ArrayList<>();
    @Override
    public void addEle(E element) {
        list.add(element);
    }
    @Override
    public void removeEle(E element) {
        list.remove(element);
    }
    @Override
    public CustomIterator<E> createCustomIterator() {
        return new ConcreteListCustomIterator(list);
    }
}

创建一个CustomIterator接口，自定义的迭代器：

/*自定义`Iterator`*/
public interface CustomIterator<E> {
    /*是否有下一个元素*/
    boolean hasNext();
    /*获取下一个元素*/
    E next();
    /*移除当期元素*/
    default void remove() {
        throw new UnsupportedOperationException("remove");
    }
}

创建一个CustomIterator接口的实现类ConcreteArrayCustomIterator<E>：

/*数组类型的迭代器*/
public class ConcreteArrayCustomIterator<E> implements CustomIterator<E> {
    private E[] array; //数据集
    private int currentIndex = 0; //当前下标
    public ConcreteArrayCustomIterator(E[] array) {
        this.array = array;
    }
    @Override
    public boolean hasNext() {
        return currentIndex < array.length;
    }
    public E next() {
        return array[currentIndex++];
    }
}

创建一个CustomIterator接口的实现类ConcreteListCustomIterator<E>：

/*列表类型的迭代器*/
public class ConcreteListCustomIterator<E> implements CustomIterator<E> {
    private List<E> list; //数据集
    private int currentIndex = -1; //当前下标
    public ConcreteListCustomIterator(List<E> list) {
        this.list = list;
    }
    @Override
    public boolean hasNext() {
        return currentIndex < list.size() - 1;
    }
    @Override
    public E next() {
        return list.get(++currentIndex);
    }
}

客户端代码：

public class Client {
    public static void main(String[] args) {
        System.out.println("================= 迭代字符串数组 ===================");
        Aggregate<String> stringAggregate = new ConcreteArrayAggregate<>(){{
            addEle("java");
            addEle("python");
            addEle("go");
            addEle("c++");
            //移除
            removeEle("java");
            removeEle("python");
        }};
        CustomIterator<String> stringCustomIterator = stringAggregate.createCustomIterator();
        while (stringCustomIterator.hasNext()){
            String next = stringCustomIterator.next();
            System.out.println("next = " + next);
        }
        System.out.println("================= 迭代数字列表 ===================");
        Aggregate<Integer> integerAggregate = new ConcreteListAggregate<>(){{
            addEle(11);
            addEle(12);
            addEle(13);
            addEle(14);
            addEle(15);
        }};
        CustomIterator<Integer> integerCustomIterator = integerAggregate.createCustomIterator();
        while (integerCustomIterator.hasNext()){
            Integer next = integerCustomIterator.next();
            System.out.println("next = " + next);
        }
    }
}

输出内容如下：

================= 迭代字符串数组 ===================
next = go
next = c++
================= 迭代数字列表 ===================
next = 11
next = 12
next = 13
next = 14
next = 15