设计模式——迭代器模式（Iterator Pattern）+ Spring相关源码

文章目录

一、迭代器模式
二、例子
- 2.1 菜鸟例子
- - 2.1.1 定义迭代器接口
  - 2.1.2 定义迭代对象接口——用于返回一个迭代器
  - 2.1.3 实现迭代对象和迭代器
  - 2.1.4 使用
- 2.2 JDK源码——ArrayList
- 2.3 Spring源码——DefaultListableBeanFactory
三、其他设计模式

一、迭代器模式

类型： 行为型模式
目的： 用于顺序访问集合对象的元素，使用者不需要知道集合对象的底层表示。

二、例子

2.1 菜鸟例子

2.1.1 定义迭代器接口

public interface Iterator {public boolean hasNext();public Object next();
}

2.1.2 定义迭代对象接口——用于返回一个迭代器

public interface Container {public Iterator getIterator();
}

2.1.3 实现迭代对象和迭代器

public class NameRepository implements Container {public String[] names = {"Robert" , "John" ,"Julie" , "Lora"};@Overridepublic Iterator getIterator() {return new NameIterator();}private class NameIterator implements Iterator {int index;@Overridepublic boolean hasNext() {if(index < names.length){return true;}return false;}@Overridepublic Object next() {if(this.hasNext()){return names[index++];}return null;}     }
}

2.1.4 使用

public class IteratorPatternDemo {public static void main(String[] args) {NameRepository namesRepository = new NameRepository();for(Iterator iter = namesRepository.getIterator(); iter.hasNext();){String name = (String)iter.next();System.out.println("Name : " + name);}  }
}

2.2 JDK源码——ArrayList

private static class ArrayList<E> extends AbstractList<E> implements RandomAccess, java.io.Serializable {@Overridepublic Iterator<E> iterator() {return new ArrayItr<>(a);}
}
private static class ArrayItr<E> implements Iterator<E> {private int cursor;private final E[] a;ArrayItr(E[] a) {this.a = a;}@Overridepublic boolean hasNext() {return cursor < a.length;}@Overridepublic E next() {int i = cursor;if (i >= a.length) {throw new NoSuchElementException();}cursor = i + 1;return a[i];}
}

2.3 Spring源码——DefaultListableBeanFactory

public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {private volatile List<String> beanDefinitionNames;private volatile Set<String> manualSingletonNames;public Iterator<String> getBeanNamesIterator() {CompositeIterator<String> iterator = new CompositeIterator();iterator.add(this.beanDefinitionNames.iterator());iterator.add(this.manualSingletonNames.iterator());return iterator;}
}

迭代器CompositeIterator

public class CompositeIterator<E> implements Iterator<E> {private final Set<Iterator<E>> iterators = new LinkedHashSet();private boolean inUse = false;public CompositeIterator() {}public void add(Iterator<E> iterator) {Assert.state(!this.inUse, "You can no longer add iterators to a composite iterator that's already in use");if (this.iterators.contains(iterator)) {throw new IllegalArgumentException("You cannot add the same iterator twice");} else {this.iterators.add(iterator);}}public boolean hasNext() {this.inUse = true;Iterator var1 = this.iterators.iterator();Iterator iterator;do {if (!var1.hasNext()) {return false;}iterator = (Iterator)var1.next();} while(!iterator.hasNext());return true;}public E next() {this.inUse = true;Iterator var1 = this.iterators.iterator();Iterator iterator;do {if (!var1.hasNext()) {throw new NoSuchElementException("All iterators exhausted");}iterator = (Iterator)var1.next();} while(!iterator.hasNext());return iterator.next();}public void remove() {throw new UnsupportedOperationException("CompositeIterator does not support remove()");}
}