给我符合下面要求的Java代码，基于 Composite 设计模式设计一个办公邮件发送程序，其主要需求如下： （1） 程序中的组织单位包括学院、系、班级、学生会构成； （2） 可以以学生个人或组织单位的名义发送邮件； （3） 邮件可以发送到任何个人或组织单位。

首先我们需要定义一个抽象基类，表示组织单位：

public abstract class Organization {
    protected String name;
    public Organization(String name) {
        this.name = name;
    }
    public abstract void sendMail(Mail mail);
}

然后定义各种组织单位的子类，例如学院、系、班级、学生会：

public class College extends Organization {
    private List<Organization> departments;
    public College(String name) {
        super(name);
        departments = new ArrayList<>();
    }
    public void addDepartment(Organization department) {
        departments.add(department);
    }
    public void removeDepartment(Organization department) {
        departments.remove(department);
    }
    @Override
    public void sendMail(Mail mail) {
        System.out.println(name + " sends a mail to " + mail.getRecipient());
        for(Organization department : departments) {
            department.sendMail(mail);
        }
    }
}

public class Department extends Organization {
    private List<Organization> classes;
    public Department(String name) {
        super(name);
        classes = new ArrayList<>();
    }
    public void addClass(Organization cls) {
        classes.add(cls);
    }
    public void removeClass(Organization cls) {
        classes.remove(cls);
    }
    @Override
    public void sendMail(Mail mail) {
        System.out.println(name + " sends a mail to " + mail.getRecipient());
        for(Organization cls : classes) {
            cls.sendMail(mail);
        }
    }
}

public class Class extends Organization {
    private List<Organization> students;
    public Class(String name) {
        super(name);
        students = new ArrayList<>();
    }
    public void addStudent(Organization student) {
        students.add(student);
    }
    public void removeStudent(Organization student) {
        students.remove(student);
    }
    @Override
    public void sendMail(Mail mail) {
        System.out.println(name + " sends a mail to " + mail.getRecipient());
        for(Organization student : students) {
            student.sendMail(mail);
        }
    }
}

public class Student extends Organization {
    public Student(String name) {
        super(name);
    }
    @Override
    public void sendMail(Mail mail) {
        System.out.println(name + " sends a mail to " + mail.getRecipient());
    }
}

最后定义邮件的类：

public class Mail {
    private Organization sender;
    private String recipient;
    private String content;
    public Mail(Organization sender, String recipient, String content) {
        this.sender = sender;
        this.recipient = recipient;
        this.content = content;
    }
    public Organization getSender() {
        return sender;
    }
    public String getRecipient() {
        return recipient;
    }
    public String getContent() {
        return content;
    }
}

可以通过组合各种组织单位构建整个组织结构，然后在需要发送邮件时调用相应的组织单位的 `sendMail` 方法即可。

示例代码：

public class Main {
    public static void main(String[] args) {
        College college = new College("College of Computer Science and Technology");
        Department dept1 = new Department("Department of Software Engineering");
        Department dept2 = new Department("Department of Computer Science");
        college.addDepartment(dept1);
        college.addDepartment(dept2);
        Class cls1 = new Class("Class of SE 1");
        Class cls2 = new Class("Class of SE 2");
        Class cls3 = new Class("Class of CS 1");
        dept1.addClass(cls1);
        dept1.addClass(cls2);
        dept2.addClass(cls3);
        Student stu1 = new Student("Alice");
        Student stu2 = new Student("Bob");
        Student stu3 = new Student("Charlie");
        Student stu4 = new Student("David");
        cls1.addStudent(stu1);
        cls1.addStudent(stu2);
        cls2.addStudent(stu3);
        cls3.addStudent(stu4);
        Mail mail1 = new Mail(stu1, "Group of SE 2", "Hello everyone!");
        Mail mail2 = new Mail(dept1, "Group of CS 1", "Meet new professor!");
        Mail mail3 = new Mail(college, "All students", "Holiday notice!");
        stu1.sendMail(mail1);
        dept1.sendMail(mail2);
        college.sendMail(mail3);
    }
}