设计模式-迭代器模式

目录

一:基本介绍

二:原理说明

三:案例说明

四:优点

五:缺点

---

一:基本介绍

1)属于行为模式

2)如果我们的集合元素是用不同的方式实现的,有数组,还有java的集合类,或者还有其他方式,当客户 端要遍历这些集合元素的时候就要使用多种遍历方式,而且还会暴露元素的内部结构,可以考虑迭代器模式解决

3)迭代器模式,提供一种遍历集合元素的统一接口,用一致的方法遍历集合元素,不需要知道集合对象的底层表示,即:不暴露其内部结构

二:原理说明

1)Iterator:迭代器接口,是系统提供,含有hasNext, next, remove

2)ConcreteIterator:具体的迭代器类,管理迭代

3)Aggregate:一个统一的聚合接口,将客户端和具体的聚合解耦

4)ConcreateAggreage:具体的聚合,持有对象集合

5)ClientL:客户端,通过Iterator和Aggregate依赖子类

三:案例说明

// 系
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Department {
    private String name;
    private String desc;
}

public class ComputerCollegeIterator implements Iterator {
    // 这里我们需要知道Department是以怎样的方式存放 ==>数组
    Department[] departments;
    // 遍历的位置
    int position = 0;

    public ComputerCollegeIterator(Department[] departments) {
        this.departments = departments;
    }

    // 判断是否还有下一个
    @Override
    public boolean hasNext() {
        if (position >= departments.length || departments[position] == null) {
            return false;
        } else {
            return true;
        }

    }

    @Override
    public Object next() {
        Department department = departments[position];
        position +=1;
        return department;
    }

    // 删除的方法默认空实现
    public void remove() {

    }
}

public class InfoColleageIterator implements Iterator {

    List<Department> departmentList;// 信息工程学院是以list的方式存放系
    int index = -1;// 索引

    public InfoColleageIterator(List<Department> departmentList) {
        this.departmentList = departmentList;
    }

    // 判断list中还有没有下一个元素
    @Override
    public boolean hasNext() {
        if (index >= departmentList.size() - 1) {
            return false;
        } else {
            index += 1;
            return true;
        }
    }

    @Override
    public Object next() {
        return departmentList.get(index);
    }

    // 空实现remove
    public void remove() {

    }
}

public class ComputerCollege implements College {
    Department[] departments;
    int numOfDepartments = 0;// 保存当前数组的个数

    public ComputerCollege() {
        departments = new Department[5];
        addDepartment("java", "java");
        addDepartment("php", "php");
        addDepartment("大数据", "大数据");
    }

    @Override
    public String getName() {
        return "计算机学院";
    }

    @Override
    public void addDepartment(String name, String desc) {
        Department department = new Department(name, desc);
        departments[numOfDepartments] = department;
        numOfDepartments++;

    }

    @Override
    public Iterator createIterator() {
        return new ComputerCollegeIterator(departments);
    }
}

public class InfoCollege implements College{

    List<Department> departmentList;

    public InfoCollege() {
        departmentList = new ArrayList<Department>();
        addDepartment("信息安全专业", "信息安全专业");
        addDepartment("网络安全专业", "网络安全专业");
        addDepartment("服务器安全专业", "服务器安全专业");
    }

    @Override
    public String getName() {
        return "信息工程学院";
    }

    @Override
    public void addDepartment(String name, String desc) {
        Department department = new Department(name, desc);
        departmentList.add(department);
    }

    @Override
    public Iterator createIterator() {
        return new InfoColleageIterator(departmentList);
    }
}

public interface College {
    public String getName();

    // 增加系的方法
    public void addDepartment(String name, String desc);

    // 返回一个迭代器遍历
    public Iterator createIterator();

}

public class OutPutImpl {
    // 学院集合
    List<College> collegeList;

    public OutPutImpl(List<College> collegeList) {
        this.collegeList = collegeList;
    }

    // 遍历所有的学院,然后调用printDepartment 输出各个学院的系
    public void printCollege() {
        // 从collegeList取出所有学院
        Iterator<College> iterator = collegeList.iterator();
        while (iterator.hasNext()) {
            // 取出一个学院
            College college = iterator.next();
            System.out.println("College: " + college.getName());
            printDepartment(college.createIterator());
        }
    }

    // 学院输出系
    public void printDepartment(Iterator iterator) {
        while (iterator.hasNext()) {
            Department department = (Department) iterator.next();
            System.out.println(department.getName());
        }

    }
}

public class Client {
    public static void main(String[] args) {
        // 创建学院
        ArrayList<College> colleges = new ArrayList<>();
        ComputerCollege computerCollege = new ComputerCollege();
        InfoCollege infoCollege = new InfoCollege();

        colleges.add(computerCollege);
        colleges.add(infoCollege);

        OutPutImpl outPut = new OutPutImpl(colleges);
        outPut.printCollege();
    }
}

四:优点

1)提供了统一的遍历方法,客户不用再考虑聚合的类型,使用一种方法就可以遍历对象了

2)隐藏了聚合的内部结构,客户端要遍历聚合的时候,只能取到迭代器,而不会周到聚合的具体组成

3)当要展示一组相似对象,或者遍历一组相同对象时使用,适合使用迭代器模式

五:缺点

每个聚合对象都要有一个迭代器,会生成许多迭代器不好管理类