用Java语言写定义一个Person类，含:姓名、性别、年龄等字段；继承Person类设计Teacher类，增加：职称、部门等字段；继承Person类设计Student类，增加：学号、班级等字段。定义各类的构造方法和toString()方法，并分别创建对象进行测试。

好的，以下是使用Java语言实现上述需求的代码：

// Person类
public class Person {
    private String name;
    private String gender;
    private int age;

    public Person(String name, String gender, int age) {
        this.name = name;
        this.gender = gender;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public String getGender() {
        return gender;
    }

    public int getAge() {
        return age;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", gender='" + gender + '\'' +
                ", age=" + age +
                '}';
    }
}

// Teacher类
public class Teacher extends Person {
    private String title;
    private String department;

    public Teacher(String name, String gender, int age, String title, String department) {
        super(name, gender, age);
        this.title = title;
        this.department = department;
    }

    public String getTitle() {
        return title;
    }

    public String getDepartment() {
        return department;
    }

    @Override
    public String toString() {
        return "Teacher{" +
                "title='" + title + '\'' +
                ", department='" + department + '\'' +
                "} " + super.toString();
    }
}

// Student类
public class Student extends Person {
    private String studentId;
    private String className;

    public Student(String name, String gender, int age, String studentId, String className) {
        super(name, gender, age);
        this.studentId = studentId;
        this.className = className;
    }

    public String getStudentId() {
        return studentId;
    }

    public String getClassName() {
        return className;
    }

    @Override
    public String toString() {
        return "Student{" +
                "studentId='" + studentId + '\'' +
                ", className='" + className + '\'' +
                "} " + super.toString();
    }
}

// 测试代码
public class Main {
    public static void main(String[] args) {
        Person person = new Person("张三", "男", 20);
        System.out.println(person);

        Teacher teacher = new Teacher("李四", "女", 30, "教授", "计算机系");
        System.out.println(teacher);

        Student student = new Student("王五", "男", 19, "20210001", "软件工程1班");
        System.out.println(student);
    }
}

运行结果如下：

Person{name='张三', gender='男', age=20}
Teacher{title='教授', department='计算机系'} Person{name='李四', gender='女', age=30}
Student{studentId='20210001', className='软件工程1班'} Person{name='王五', gender='男', age=19}