90 lines
2.0 KiB
Java
90 lines
2.0 KiB
Java
## 迭代器（Iterator）
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### Intent
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提供一种顺序访问聚合对象元素的方法，并且不暴露聚合对象的内部表示。
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### Class Diagram
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- Aggregate 是聚合类，其中 createIterator() 方法可以产生一个 Iterator；
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- Iterator 主要定义了 hasNext() 和 next() 方法；
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- Client 组合了 Aggregate，为了迭代遍历 Aggregate，也需要组合 Iterator。
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/image-20201102012333804.png" alt="image-20191130164425351" style="zoom: 67%;" /> </div><br>
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### Implementation
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```java
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public interface Aggregate {
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Iterator createIterator();
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}
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```
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```java
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public class ConcreteAggregate implements Aggregate {
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private Integer[] items;
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public ConcreteAggregate() {
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items = new Integer[10];
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for (int i = 0; i < items.length; i++) {
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items[i] = i;
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}
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}
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@Override
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public Iterator createIterator() {
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return new ConcreteIterator<Integer>(items);
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}
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}
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```
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```java
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public interface Iterator<Item> {
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Item next();
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boolean hasNext();
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}
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```
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```java
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public class ConcreteIterator<Item> implements Iterator {
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private Item[] items;
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private int position = 0;
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public ConcreteIterator(Item[] items) {
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this.items = items;
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}
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@Override
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public Object next() {
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return items[position++];
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}
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@Override
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public boolean hasNext() {
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return position < items.length;
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}
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}
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```
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```java
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public class Client {
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public static void main(String[] args) {
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Aggregate aggregate = new ConcreteAggregate();
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Iterator<Integer> iterator = aggregate.createIterator();
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while (iterator.hasNext()) {
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System.out.println(iterator.next());
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}
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}
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}
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```
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### JDK
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- [java.util.Iterator](http://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html)
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- [java.util.Enumeration](http://docs.oracle.com/javase/8/docs/api/java/util/Enumeration.html)
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