定义
提供一个对象来顺序访问聚合对象中的一系列数据,而不暴露聚合对象的内部表示。
结构
- 抽象聚合角色(Aggregate):定义存储、添加、删除聚合元素以及创建迭代器对象的接口。
- 具体聚合角色(ConcreteAggregate):实现抽象聚合类,返回一个具体的迭代器实例。
- 抽象迭代器角色(Iterator):定义访问和遍历聚合元素的接口,通常包含hasNext()、next()等方法。
- 具体迭代器角色(ConcreteIterator):实现抽象迭代器接口中所定义的方法,完成对聚合对象的遍历,记录遍历的当前位置。
案例
定义一个可以存储学生对象的容器,将遍历该容器的功能交由迭代器实现。
学生类
package com.hupp.iterator;
public class Student {
public Student() {
}
public Student(String name, String number) {
this.name = name;
this.number = number;
}
private String name;
private String number;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getNumber() {
return number;
}
public void setNumber(String number) {
this.number = number;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", number='" + number + '\'' +
'}';
}
}
抽象聚合角色类
package com.hupp.iterator;
/**
* 抽象聚合角色类
*/
public interface StudentAggregate {
void addStudent(Student student);
void removeStudent(Student student);
StudentIterator getStudentIterator();
}
具体聚合角色
package com.hupp.iterator;
import java.util.ArrayList;
import java.util.List;
public class StudentAggregateImpl implements StudentAggregate {
private List<Student> list = new ArrayList<>();
@Override
public void addStudent(Student student) {
list.add(student);
}
@Override
public void removeStudent(Student student) {
list.remove(student);
}
@Override
public StudentIterator getStudentIterator() {
return new StudentIteratorImpl(list);
}
}
抽象迭代器类
package com.hupp.iterator;
/**
* 抽象迭代器
*/
public interface StudentIterator {
boolean hasNext();
Student next();
}
具体迭代器
package com.hupp.iterator;
import java.util.List;
/**
* 具体迭代器
*/
public class StudentIteratorImpl implements StudentIterator{
public StudentIteratorImpl(List<Student> list) {
this.list = list;
}
private List<Student> list;
private int position=0;//用来记录遍历时的位置
@Override
public boolean hasNext() {
return position<list.size();
}
@Override
public Student next() {
Student currentStudent = list.get(position);
position++;
return currentStudent;
}
}
客户端
package com.hupp.iterator;
public class Client {
public static void main(String[] args) {
//创建聚合对象
StudentAggregateImpl aggregate = new StudentAggregateImpl();
aggregate.addStudent(new Student("张三","001"));
aggregate.addStudent(new Student("李四","002"));
aggregate.addStudent(new Student("王五","003"));
aggregate.addStudent(new Student("赵六","004"));
StudentIterator iterator = aggregate.getStudentIterator();
while (iterator.hasNext()){
Student student = iterator.next();
System.out.println(student.toString());
}
}
}