迭代器模式

iterator模式
需求：给大家举个例子，现在假设，有一个教室类，里面包含了一堆学生，我现在要遍历教室里的学生，怎么来玩儿

public interface Aggregate {
    public abstract Iterator iterator(); 
}

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

public class Student {
    
    private String name;
    
    public Student (String name) {
        this.name = name;
    }
    
    public String getName() {
        return name;
    }
    
}


public class Classroom implements Aggregate {
    private Student[] students;
    private int last = 0;

    public Classroom(int size) {
        this.students = new Student[size];
    }

    public Student getStudents(int size) {
        return students[size];
    }

    public void addStudent(Student student) {
        this.students[last] = student;
        last++;
    }

    public int getLength() {
        return last;
    }

    @Override
    public Iterator iterator() {
        return new ClassroomIterator(this);
    }


}

public class ClassroomIterator implements Iterator {
    private Classroom classroom;
    private int index;

    public ClassroomIterator(Classroom classroom) {
        this.classroom = classroom;
        this.index = 0;
    }

    @Override
    public boolean hasNext() {
        if (index < classroom.getLength()) {
            return true;
        } else {
            return false;
        }
    }

    @Override
    public Object next() {
        Student student=classroom.getStudents(index);
        index++;
        return student;
    }
}

public class Main {

    public static void main(String[] args) {
        Classroom classroom = new Classroom(2);
        classroom.addStudent(new Student("小李"));
        classroom.addStudent(new Student("王三"));
        Iterator iterator = classroom.iterator();
        while (iterator.hasNext()){
            System.out.println(((Student)iterator.next()).getName());
        }

    }
}

面向Iterator接口编程，无论底层的数据结构和迭代算法如何变化，调用者都不用修改代码
高内聚，低耦合，漂亮
其实一般很少自己写这个iterator模式的，一般都是在集合编程中使用，尤其是如果要对集合元素遍历过程中做插入删除操作，那就用iterator，体验JDK已经封装好的iterator模式，加深印象，如果要对某个类中的集合进行遍历，由那个集合类返回一个iterator回来，我们统一面向iterator迭代器接口来编程遍历，提高系统整体的可维护性，可扩展性
如果自己写iterator模式，一般是研发底层的框架，比如提供某个数据给外部遍历，那么可以使用iterator模式自己封装迭代器，以后阶段如果有机会，我们也会去实践