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设计模式：迭代器模式

news 来源：原创 2024/9/22 21:27:52

迭代器模式的示例可以涵盖各种数据结构的遍历，包括数组、列表、树、图等。下面是一些不同场景下迭代器模式的示例及其代码实现。

示例 1: 数组遍历

使用迭代器模式遍历数组。

// 迭代器接口
interface Iterator<T> {boolean hasNext();T next();
}// 数组迭代器
class ArrayIterator<T> implements Iterator<T> {private T[] array;private int currentIndex = 0;public ArrayIterator(T[] array) {this.array = array;}@Overridepublic boolean hasNext() {return currentIndex < array.length;}@Overridepublic T next() {if (!hasNext()) {throw new NoSuchElementException();}return array[currentIndex++];}
}// 客户端代码
public class ArrayIteratorExample {public static void main(String[] args) {Integer[] numbers = {1, 2, 3, 4, 5};Iterator<Integer> iterator = new ArrayIterator<>(numbers);while (iterator.hasNext()) {Integer number = iterator.next();System.out.println(number);}}
}

示例 2: 二叉树的深度优先遍历

二叉树的深度优先遍历（使用栈实现）。

// 树节点
class TreeNode<T> {T value;TreeNode<T> left;TreeNode<T> right;TreeNode(T value) {this.value = value;}
}// 树的迭代器
class BinaryTreeIterator<T> implements Iterator<T> {private Stack<TreeNode<T>> stack = new Stack<>();public BinaryTreeIterator(TreeNode<T> root) {pushLeft(root);}private void pushLeft(TreeNode<T> node) {while (node != null) {stack.push(node);node = node.left;}}@Overridepublic boolean hasNext() {return !stack.isEmpty();}@Overridepublic T next() {if (!hasNext()) {throw new NoSuchElementException();}TreeNode<T> node = stack.pop();pushLeft(node.right);return node.value;}
}// 客户端代码
public class BinaryTreeIteratorExample {public static void main(String[] args) {TreeNode<Integer> root = new TreeNode<>(1);root.left = new TreeNode<>(2);root.right = new TreeNode<>(3);root.left.left = new TreeNode<>(4);root.left.right = new TreeNode<>(5);Iterator<Integer> iterator = new BinaryTreeIterator<>(root);while (iterator.hasNext()) {Integer value = iterator.next();System.out.println(value);}}
}

示例 3: 分页遍历

在分页查询场景中使用迭代器模式。

// 分页迭代器
class PagingIterator<T> implements Iterator<T> {private Iterator<T> currentIterator;private int pageSize;private int currentPage = 0;private Supplier<List<T>> pageSupplier;public PagingIterator(int pageSize, Supplier<List<T>> pageSupplier) {this.pageSize = pageSize;this.pageSupplier = pageSupplier;fetchNextPage();}private void fetchNextPage() {List<T> page = pageSupplier.get();currentIterator = page.iterator();currentPage++;}@Overridepublic boolean hasNext() {if (currentIterator.hasNext()) {return true;}fetchNextPage(); // 尝试获取下一页return currentIterator.hasNext();}@Overridepublic T next() {if (!hasNext()) {throw new NoSuchElementException();}return currentIterator.next();}
}// 模拟分页数据提供函数
Supplier<List<Integer>> pageSupplier = new Supplier<List<Integer>>() {private int totalPages = 5;private int currentPage = 0;@Overridepublic List<Integer> get() {if (currentPage < totalPages) {currentPage++;return Arrays.asList(1, 2, 3); // 模拟每页的数据}return Collections.emptyList();}
};// 客户端代码
public class PagingIteratorExample {public static void main(String[] args) {Iterator<Integer> iterator = new PagingIterator<>(3, pageSupplier);while (iterator.hasNext()) {Integer number = iterator.next();System.out.println(number);}}
}