完善下列代码：public class Student { private int id; private String name; private int classId; private int teacherId; // 构造函数、Getter和Setter方法 } public class Class { private int id; private String name; private int teacherId; // 构造函数、Getter和Setter方法 } public class Teacher { private int id; private String name; // 构造函数、Getter和Setter方法 }

下面是完整的代码：

public class Student {
    private int id;
    private String name;
    private int classId;
    private int teacherId;

    public Student(int id, String name, int classId, int teacherId) {
        this.id = id;
        this.name = name;
        this.classId = classId;
        this.teacherId = teacherId;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public int getClassId() {
        return classId;
    }

    public void setClassId(int classId) {
        this.classId = classId;
    }

    public int getTeacherId() {
        return teacherId;
    }

    public void setTeacherId(int teacherId) {
        this.teacherId = teacherId;
    }
}

public class Class {
    private int id;
    private String name;
    private int teacherId;

    public Class(int id, String name, int teacherId) {
        this.id = id;
        this.name = name;
        this.teacherId = teacherId;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public int getTeacherId() {
        return teacherId;
    }

    public void setTeacherId(int teacherId) {
        this.teacherId = teacherId;
    }
}

public class Teacher {
    private int id;
    private String name;

    public Teacher(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

在每个类中，我们定义了构造函数和Getter/Setter方法来设置和获取私有变量。这些方法使得我们可以封装这些类并从其他类中访问它们的属性。