Java中迭代器的實現

此處用鏈表來示範

1.先創建一個鏈表類

public class LinkedList<T> implements Iterable<T> {

    private Node<T> head;
    private Node<T> tail;

    public static <T> LinkedList<T> newEmptyList() {
        return new LinkedList<T>();
    }

    private LinkedList() {
        head = null;
        tail = null;
    }

    public void add(T value) {
        Node<T> node = new Node<>(value);
        if (tail == null) {
            head = node;
        } else {
            tail.setNext(node);
        }
        tail = node;
    }
 }
class Node<T> {
    private final T value;
    private Node next;

    public Node(T value) {
        this.value = value;
        this.next = null;
    }

    public T getValue() {
        return value;
    }

    public Node getNext() {
        return next;
    }

    public void setNext(Node next) {
        this.next = next;
    }
}

2.我們給LinkedList類實現Iterable<T>接口

然後實現其方法

    @Override
    public Iterator<T> iterator() {
        return null;
    }

3.新建內部類並且實現Iterator<T>接口

private class ListIterator implements Iterator<T> {
        private Node<T> currentNode;

        public ListIterator(Node<T> head) {
            currentNode = head;
        }

        @Override
        public boolean hasNext() {
            return currentNode != null;
        }

        @Override
        public T next() {
            if (currentNode == null) {
                throw new NoSuchElementException();
            }
            T value = currentNode.getValue();
            currentNode = currentNode.getNext();
            return value;
        }

        @Override
        public void remove() {

        }
    }

此處只實現了next和hasNext，remove可自行實現，我們可以看到，迭代器其實就是對數據進行了封裝，使得每次可以獲取一個數據。

4.將此內部類返回

    @Override
    public Iterator<T> iterator() {
        return new ListIterator(head);
    }

5.最終代碼

package cn.chenmixuexi;

import java.util.Iterator;
import java.util.NoSuchElementException;

public class LinkedList<T> implements Iterable<T> {

    private Node<T> head;
    private Node<T> tail;

    public static <T> LinkedList<T> newEmptyList() {
        return new LinkedList<T>();
    }

    private LinkedList() {
        head = null;
        tail = null;
    }

    public void add(T value) {
        Node<T> node = new Node<>(value);
        if (tail == null) {
            head = node;
        } else {
            tail.setNext(node);
        }
        tail = node;
    }

    private class ListIterator implements Iterator<T> {
        private Node<T> currentNode;

        public ListIterator(Node<T> head) {
            currentNode = head;
        }

        @Override
        public boolean hasNext() {
            return currentNode != null;
        }

        @Override
        public T next() {
            if (currentNode == null) {
                throw new NoSuchElementException();
            }
            T value = currentNode.getValue();
            currentNode = currentNode.getNext();
            return value;
        }

        @Override
        public void remove() {
        }
    }

    @Override
    public Iterator<T> iterator() {
        return new ListIterator(head);
    }
}
class Node<T> {
    private final T value;
    private Node next;

    public Node(T value) {
        this.value = value;
        this.next = null;
    }

    public T getValue() {
        return value;
    }

    public Node getNext() {
        return next;
    }

    public void setNext(Node next) {
        this.next = next;
    }
}