第二节：迭代器模式——迭代器模式应用

一、应用实例

　　1、应用实例要求

　　　　编写程序展示一个学校院系结构：需求是这样，要在一个页面中展示出学校的院系组成，一个学校有多个学院，一个学院有多个院系。

　　2、设计思路分析

　　

二、代码实现

　　院系类：Element 即容器中存放的，需要来遍历的单位

/**
 * 院系
 */
public class Department {

    private String name;
    private String desc;

    public Department(String name, String desc) {
        this.name = name;
        this.desc = desc;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDesc() {
        return desc;
    }

    public void setDesc(String desc) {
        this.desc = desc;
    }
}

　　用来遍历计算机学院的 迭代器：

/**
 * ComputerCollegeIterator 以数组方式存放
 */
public class ComputerCollegeIterator implements Iterator {

    /**
     *  这里我们需要知道 Department 是以怎样的方式存放
     */
    Department[] departments;
    int position = 0;  //遍历的位置


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

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


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

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

    }
}

　　用来遍历信息工程学院的 迭代器：

public class InfoCollegeIterator implements Iterator {

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

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

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

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

    @Override
    public void remove() {

    }
}

　　学院的接口：

/**
 * 学院的接口
 */
public interface College {

    public String getName();

    /**
     * 增加院系的方法
     * @param name
     * @param desc
     */
    public void addDepartment(String name, String desc);

    /**
     * 返回一个迭代器，遍历
     * @return
     */
    public Iterator createIterator();
}

　　计算机学院：

public class ComputerCollege implements College{

    Department[] departments;
    int numOfDepartment = 0; //保存当前数组的对象个数

    public ComputerCollege() {
        departments = new Department[5];
        addDepartment("Java", "Java专业");
        addDepartment("C语言", "C专业");
        addDepartment("大数据", "大数据专业");
    }

    @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[numOfDepartment++] = department;
    }

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

　　信息工程学院：

public class InfoCollege implements College{

    List<Department> departmentsList;

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

    @Override
    public Iterator createIterator() {
        return new InfoCollegeIterator(departmentsList);
    }
}

　　封装一个用于输出的学校信息的类：

public class OutputImpl {

    /**
     * 学院集合
     */
    List<College> collegeList;

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

    /**
     * 遍历所有学院，然后调用 printDepartment 输出各个学院的系
     */
    public void printCollege() {
        // 从 collegeList 取出所有学院，Java 中的 List 已经实现了Iterator接口
        Iterator<College> iterator = collegeList.iterator();

        while (iterator.hasNext()) {
            //取出一个学院
            College college = iterator.next();
            System.out.println("========"+ college.getName() +"==========");
            printDepartment(college.createIterator());
        }

    }

    /**
     * 输出学院下面的院系
     */
    public void printDepartment(Iterator iterator) {
        while (iterator.hasNext()) {
            Department dept = (Department)iterator.next();
            System.out.println(dept.getDesc());
        }
    }
}

　　客户端：

public class Client {
    public static void main(String[] args) {

        //创建学院
        List<College> colleges = new ArrayList<>();
        colleges.add(new ComputerCollege());
        colleges.add(new InfoCollege());

        OutputImpl output = new OutputImpl(colleges);
        output.printCollege();
    }
}