Java 设计模式(13) -- 迭代器

Intent
Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

How to
Iterator
defines an interface for accessing and traversing elements.

ConcreteIterator
implements the Iterator interface.
keeps track of the current position in the traversal of the aggregate.

Aggregate
defines an interface for creating an Iterator object.

ConcreteAggregate
implements the Iterator creation interface to return an instance of the proper ConcreteIterator.

Known cases
Java Collection Library

UML

 

 

代码样例：

package org.haha.DesignPatterns.iterator; public class Person { private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } public Person(String name) { this.name = name; } @Override public int hashCode() { final int PRIME = 31; int result = 1; result = PRIME * result + ((name == null) ? 0 : name.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; final Person other = (Person) obj; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; return true; } } package org.haha.DesignPatterns.iterator; import java.util.ArrayList; import java.util.Collections; import java.util.Iterator; import java.util.List; public class PersonList { private List<Person> persons = new ArrayList<Person>(); public boolean addPerson(Person p) { return persons.add(p); } public boolean removePerson(Person p) { return persons.remove(p); } public Iterator<Person> createIterator() { return new PersonIterator(this); } List<Person> getPersons() { return Collections.unmodifiableList(persons); } } package org.haha.DesignPatterns.iterator; import java.util.Iterator; public class PersonIterator implements Iterator<Person> { private final PersonList persons; private int currentIndex = 0; public PersonIterator(PersonList persons) { this.persons = persons; } public boolean hasNext() { return persons.getPersons().size() - 1 >= currentIndex; } public Person next() { return persons.getPersons().get(currentIndex++); } public void remove() { throw new UnsupportedOperationException(); } } package org.haha.DesignPatterns.iterator; import java.util.Iterator; public class TestIterator { public static void main(String[] args) { PersonList persons = new PersonList(); for (int i = 0; i < 10; i++) { Person p = new Person("name" + i); persons.addPerson(p); } Iterator<Person> iter = persons.createIterator(); while (iter.hasNext()) { Person p = iter.next(); System.out.println(p.getName()); } } }