java - 此代码运行是否需要 getter 和 setter？

Question

我在下面包含了我的所有代码(5 个类(class))，用于一个简单的学生数据库。

我与相信在 Name、Address 和 Student 类中有必要包含所有 getter 的人共同编写了这段代码和目前在那里的二传手。我认为代码在没有它们的情况下也能正常工作，并且它们不是必需的并且应该被删除？如果它们是必要的，有人可以解释为什么或者有人可以确认它们不是必需的吗？

地址类

public class Address {

private String street, area, city, country;

public Address(String street, String area, String city, String country) {
    this.street = street;
    this.area = area;
    this.street = city;
    this.country = country;
}

public void setStreet(String street) {
    this.street = street;
}

public void setArea(String area) {
    this.area = area;
}

public void setCity(String city) {
    this.city = city;
}

public void setCountry(String country) {
    this.country = country;
}

public String street() {
    return street;
}

public String area() {
    return area;
}

public String city() {
    return city;
}

public String country() {
    return country;
}

    /** Returns area, street, city and country concatenated together respectively */
public String toString() {
    return area + ", " + street + ", " + city + ", " + country + ".";
}

    }

名称类

public class Name{

private String firstName, lastName;

public Name (String firstName, String lastName){
    this.firstName = firstName;
    this.lastName = lastName;
}

public void setFirstName(String firstName){
    this.firstName = firstName;
}

public void setLastName(String lastName){
    this.lastName = lastName;
}

public String getFirstName() {
    return firstName;
}

public String getLastName() {
    return lastName;
}

/** Returns first name concatenated to last name */
public String toString() {
    return firstName + " " + lastName;
}

}

学生类(class)

     public class Student {
    private Name name; // This is calling from the Name class, giving it the               name 'name'
    private Address address; // This calls from Address, giving it the name 'address'

    private char gender;

    private String course, college;

    private int gradePointAverage, id, age, level;

    public Student(int id, String firstName, String lastName, String street, String area, String city, String country, int age, char gender, String college, String course,  int level, int gradePointAverage){ //This is the list of variables called from the Student class
        this.id = id;
        this.name = new Name(firstName, lastName);
        this.address = new Address(street, area, city, country);
        this.age = age;
        this.gender = gender;
        this.college = college;
        this.course = course;
        this.level = level;
        this.gradePointAverage = gradePointAverage;
    }

    public int getId(){
        return id;
    }

    public String getName(){
        return name.toString();
    }

    public String getAddress(){
        return address.toString();
    }

    public int getAge(){
        return age;
    }

    public char getGender(){
        return gender;
    }

    public String getCollege(){
        return college;
    }

    public int getLevel() {
        return level;
    }

     public String getCourse() {
        return course;
    }

    public int getGradePointAverage() {
        return gradePointAverage;
    }

    public void printStudent() {
        System.out.println("The Student " + name.toString() + " is logged under the student ID number " + id + ".");
        System.out.println("They live at " + address.toString() + " and their age is " + age + ".");
        System.out.println("Their gender is " + gender + ".");
        System.out.println("The student studies at " + college + " attending classes in " + course + ".");
        System.out.println("Their level is " + level + " and the student grade average in points is " + gradePointAverage + ".");
        System.out.println();
    }

    }

大学社区类

    import java.util.*;

public class CollegeCommunity

    {

    private ArrayList<Student> students; // Setting up an arraylist to store student details




        public CollegeCommunity()

            {
                students = new ArrayList<Student>();
            }


        public void addStudent(Student student) // adds a student.

            {
                students.add(student); // .add method command.
            }


        public void removeStudent(int id) // deleting a student, after being passed id to locate desired student.

            {
                for (int i=0; i<students.size(); i++ ){ // using a loop to decide what student to remove by matching the student ID which was passed to the method with the student ID's on record. Once there's a match, the student will be removed (.remove).
                    if(students.get(i).getId()==id) {
                        students.remove(i);
                    }
                }
            }


        public void showStudent(int id) // same as remove above but instead using print command to view details of particular student.

            {
                for (int i=0; i<students.size(); i++ ){
                    if(students.get(i).getId()==id) {
                        students.get(i).printStudent();
                   }
                }
            }


        public void showAllStudents()

            {
                for (int i=0; i<students.size(); i++ ){ // This loop command will display ALL student details as no specific ID was passed, so it will run as long as value 'i' is less than student.size.
                    int id=students.get(i).getId();
                        showStudent(id);
                }
            }


        public void showStudentsInCourse(String course) // This will show students in a particular course.

            {
                for(int i=0; i<students.size(); i++ ){ // Loop is same as remove but comparing the string course with the course of each student. .equals is used to compare strings.
                    if(students.get(i).getCourse().equals(course)){
                        int id=students.get(i).getId();
                            showStudent(id);
                    }
                }
            }


        public int calculateGradePointAverage() // calculating the grade point average as a percentage

        {
            int total = 0;
            for (int i = 0; i < students.size(); i++ ){
                total = total + students.get(i).getGradePointAverage(); // total is calculated as it loops, each students score (getGradePointAverage).
            }

            total = total / students.size(); // final figure is total divided by the number of students, to give an average score.

            return total;

        }
}

测试系统类

    import java.util.*;

    public class TestSystem

{
   public static void main(String[] args)

    {

        Scanner sc = new Scanner(System.in);

        Student student;
        CollegeCommunity collegeCommunity = new CollegeCommunity(); // New CollegeCommunity created called 'collegeCommunity'.

        int id, age, level, gradePointAverage; // ints created for student id, age, level of course, and the grade point value

        String fName,lName, street, area, city, country, course, college; // first name, last name strings created

        char gender; // character gender created

        boolean finish = false; // boolean finish has value of False.

            do

             {
                switch(getMenu())

                {

                    case '1':


                        System.out.println();

                        System.out.print("Please enter a new Student ID > ");
                        id = sc.nextInt();
                        sc.nextLine();

                        System.out.println();

                        System.out.print("Please enter the Student's first name > ");
                        fName = sc.nextLine();

                        System.out.println();

                        System.out.print("Please enter the Student's last name > ");
                        lName = sc.nextLine();

                        System.out.println();

                        System.out.print("Please enter the street > ");
                        street = sc.nextLine();

                        System.out.println();

                        System.out.print("Please enter the area > ");
                        area = sc.nextLine();

                        System.out.println();

                        System.out.print("Please enter the city > ");
                        city = sc.nextLine();

                        System.out.println();

                        System.out.print("Please enter the country > ");
                        country = sc.nextLine();

                        System.out.println();

                        System.out.print("Please enter the age > ");
                        age = sc.nextInt();

                        sc.nextLine();

                        System.out.println();

                        System.out.print("Please enter the gender > ");
                        gender = sc.nextLine().charAt(0);

                        System.out.println();

                        System.out.print("Please enter the college > ");
                        college = sc.nextLine();

                        System.out.println();

                        System.out.print("Please enter the course > ");
                        course = sc.nextLine();

                        System.out.println();

                        System.out.print("Please enter level > ");
                        level = sc.nextInt();

                        sc.nextLine();

                        System.out.println();

                        System.out.print("Please enter the average grade in points [0-100] > ");
                        gradePointAverage = sc.nextInt();

                        sc.nextLine();

                        System.out.println();

                        student = new Student(id, fName, lName, street, area, city, country, age, gender, college, course, level, gradePointAverage);
                        collegeCommunity.addStudent(student);


                        break;


                    case '2':


                        System.out.println();

                        System.out.print("Please enter the student ID number > ");
                        id = sc.nextInt();

                        sc.nextLine();
                        // this will delete the student selected
                        collegeCommunity.removeStudent(id);

                        System.out.println();

                        System.out.print("Student " + id + " has been deleted.");

                        System.out.println();
                        System.out.println();

                        break;


                    case '3':


                        System.out.println();

                        System.out.print("Please enter the student ID number > ");
                        id = sc.nextInt();

                        sc.nextLine();
                        // This will allow for the details of the selected student to be displayed. Calls stored data from community college.
                        collegeCommunity.showStudent(id);

                        System.out.println();
                        System.out.println();

                        break;


                    case '4':


                        System.out.println();
                        // This will show all of the students stored in the system.
                        collegeCommunity.showAllStudents();

                        System.out.println();

                        break;


                    case '5':

                        System.out.println();

                        System.out.print("Please enter the course > ");
                        course = sc.nextLine();
                        // This will show students that are enrolled in a chosen course.
                        collegeCommunity.showStudentsInCourse(course);

                        System.out.println();

                        break;

                    case '6':

                        System.out.println();

                        System.out.print("The Average grade score is " + collegeCommunity.calculateGradePointAverage() + "%");

                        System.out.println();

                        break;

                    case 'x':
                    case 'X':

                        finish = true; // boolean value changes to true if X is selected

                        System.exit(0);

                    break;

                        default:

                        System.out.println();

                        System.out.println("That is an invalid selection.");

                        System.out.println("      Please try again");

                    break;

                    }

        }while (!finish);

    }

        public static char getMenu()

            {
                Scanner sc = new Scanner(System.in);

                System.out.println();

                System.out.println("This is your community college menu");
                System.out.println("Please select from the menu options below");

                System.out.println();

                System.out.println("1 Add a Student");

                System.out.println();

                System.out.println("2 Delete a Student");

                System.out.println();

                System.out.println("3 Show details on an individual student");

                System.out.println();

                System.out.println("4 Show details on all students");

                System.out.println();

                System.out.println("5 Shows details on all students on a course");

                System.out.println();

                System.out.println("6 Display the average grade (points)");

                System.out.println();

                System.out.println("X Exit");

                System.out.println();
                System.out.println();

                System.out.print("Please make selection > ");

                return sc.next().charAt(0);
            }

    }

Answer 1

您始终可以将属性设置为 public 或 protected 或使用默认范围并访问它们(前提是类在适当的包中)

myStudent.age = 9;

也就是说，使用 setter 和 getter 总是好的做法。它简化了对设置哪些值的控制。例如。你可以在你的集合中检查，这样年龄就不会小于 4

public void setAge(int age) throws Exception {
  if (age <= 3) {
    throw new Exception("Age must be more than 3");
  }
  this.age = age;
}

用属性设置这个留给程序员，他们可能会错过代码中某处的检查。稍后调试非常棘手。

Setter 和 getter 还有助于添加日志/断点以检查程序的行为。

大多数像样的 IDE 都允许您仅从属性中自动编写 setter 和 getter 代码，所以这没什么大不了的。

作为旁注，我通常建议在需要时存储出生日期并计算年龄，因为年龄是一个会发生变化的值，而出生日期不会，而且您始终可以根据出生日期计算年龄，但不能相反。