在此示例中，我想将学校的学生添加到 ArrayList 中，并从另一个类中定义的另一个方法打印具有多态格式的数组列表。
import java.util.ArrayList;
class Student{
public static String name;
public static String gender;
public static int age;
//setting default values for the member variables
public Student(){
name = "default name";
gender = "default gender";
age = 0;
}
//constructor of the parameters for the name, gender, and age.
public Student(String name, String gender, int age){
Student.name = name;
Student.gender = gender;
Student.age = age;
}
// Polymorphism to print with a specific format
public static void printInfo(){
System.out.println(name+", "+gender+", "+age+"n");
}
}
// creating a class for Male students
class Male extends Student{
private static String gender;
public Male(String name, int age){
super(name, gender, age);
Male.gender = "Male";
}
}
// creating a class for Female students
class Female extends Student{
private static String gender;
public Female(String name, int age){
super(name, gender, age);
Female.gender = "Female";
}
}
// create a class for school to collect all the students
class School{
static ArrayList<Student> students;
public static void addStudent(Student a){
ArrayList<Student> students = new ArrayList<Student>();
students.add(a);
}
public void printAllInfo(){
//call the Student.printInfo method from the Student class
}
}
public class SchoolBuilder{
public static void main(String[] args){
School.addStudent(new Male("Sam",13));
School.addStudent(new Male("John",11));
School.addStudent(new Female("Elle",12));
School.addStudent(new Male("Paul",12));
School.addStudent(new Female("Javinia",11));
School.addStudent(new Male("Paperino",12));
//PRint all by calling School.printAllInfo should print the formatted ArrayList
}
}
输出应如下所示：
Sam, Male, 13
John, Male, 11
Elle, Female, 12
Paul, Male, 12
Javinia, Female, 11
Paperino, Male, 12
我是 JAVA 的新手，只是不知道该怎么做。这似乎很容易。 我为性别制作了这两个类，因为以后很容易添加所有男性或女性的 CSV 文件，并将它们添加到分别调用男性和女性类的数据集中。
感谢您的时间和帮助。
通常，我们通过重写某个类的toString()方法，然后打印它来做到这一点。
以下作为建设性的批评：这里有一堆问题。
- 在这种情况下，您希望避免使用静态上下文，因为静态 变量属于一个类。不是每个学生都会有相同的 例如，名称。
- 同样，您不会打电话给
Student.function()，而是会打电话给this.function()，只为那个学生打电话，而不是班上的学生。this是学生的一个实例。 - 你绝对不想在你的addStudent((方法中做
ArrayList<Student> students = new ArrayList<Student>();。你是 每次添加学生时重置学生列表。保持 在类级别声明中或更好的是，添加一个 构造 函数。
import java.util.ArrayList;
class Student{
public String name;
public String gender;
public int age;
//setting default values for the member variables
public Student(){
name = "default name";
gender = "default gender";
age = 0;
}
//constructor of the parameters for the name, gender, and age.
public Student(String name, String gender, int age){
this.name = name;
this.gender = gender;
this.age = age;
}
// Polymorphism to print with a specific format
public String printInfo(){
return name+", "+gender+", "+age+"n";
}
}
// creating a class for Male students
class Male extends Student{
private static String gender;
public Male(String name, int age){
super(name, gender, age);
Male.gender = "Male";
}
}
// creating a class for Female students
class Female extends Student{
private static String gender;
public Female(String name, int age){
super(name, gender, age);
Female.gender = "Female";
}
}
// create a class for school to collect all the students
class School{
ArrayList<Student> students = new ArrayList<Student>();
public void addStudent(Student a) {
students.add(a);
}
public void printAllInfo(){
//call the Student.printInfo method from the Student class
}
public String toString() {
String string = "";
for (Student s : students) {
string += s.printInfo();
}
return string;
}
}
public class Work{
public static void main(String[] args){
School sch = new School();
sch.addStudent(new Male("Sam",13));
sch.addStudent(new Male("John",11));
sch.addStudent(new Female("Elle",12));
sch.addStudent(new Male("Paul",12));
sch.addStudent(new Female("Javinia",11));
sch.addStudent(new Male("Paperino",12));
System.out.println(sch.toString());
}
}
您的实现中存在一些错误：
Student对象不应具有static字段。static意味着它们不是引用特定对象，而是引用类本身。
该对象是类的特定实现。您定义一个Student类来定义学生的外观，通过特定的设置，您可以创建一个学生。
当你宣布班级时，你说一个学生一般有名字、性别和年龄。
当你使用构造函数(new Student("Sam", "Male", 13)(来定义学生时，你定义了特定的实现。
class Student {
public String name;
public String gender;
public int age;
//setting default values for the member variables
public Student(){
name = "default name";
gender = "default gender";
age = 0;
}
//constructor of the parameters for the name, gender, and age.
public Student(String name, String gender, int age){
this.name = name;
this.gender = gender;
this.age = age;
}
- 类
Male和Female必须更改。扩展Student类以将默认值设置为gender字段并没有错。例如，如果Male类有一个特定的字段(例如favouriteSoccerPlayer(，而普通学生不应该有一个特定的字段，那么扩展它会更有用。在这种情况下，Male类将从父类(Student(继承字段并添加另一个额外的字段：
class Male extends Student {
private String favouriteSoccerPlayer;
public Male(String name, int age) {
super(name, "Male", age); // call the constructor of the super class
}
public Male(String name, int age, String favouriteSoccerPlayer) {
super(name, "Male", age); // call the constructor of the super class
this.favouriteSoccerPlayer = favouriteSoccerPlayer;
}
// getter and setter for only this field
}
然后，您可以执行如下操作：
Male male = new Male("John", 32, "Maradona");
System.out.println(male.getName());
您将调用Male对象从Student类继承的方法。
这将是类男性，同样是女性：
// creating a class for Male students
class Male extends Student{
private static final String gender = "Male";//This should be constant for all instances of class and because of that it is "static final"
public Male(String name, int age){
super(name, gender, age);
}
}
下一所学校不会有任何静态的东西。
import java.util.ArrayList;
// create a class for school to collect all the students
class School {
private ArrayList<Student> students; //Should not be static, and initialization moved in constructor
public School() {
students = new ArrayList<>();
}
public void addStudent(Student a) {
students.add(a);
}
public void printAllInfo() {
for (Student s : students) {
s.printInfo();
}
}
}
最后，主类应该创建学校实例，添加学生并打印他们：
public class SchoolBuilder{
public static void main(String[] args){
School school=new School();
school.addStudent(new Male("Sam",13));
school.addStudent(new Male("John",11));
school.addStudent(new Female("Elle",12));
school.addStudent(new Male("Paul",12));
school.addStudent(new Female("Javinia",11));
school.addStudent(new Male("Paperino",12));
school.printAllInfo();
}
}
最后，学生中的此方法不应在字符串中具有，因为它将再添加一个新行。
// Polymorphism to print with a specific format
public void printInfo(){
System.out.println(name+", "+gender+", "+age+"n");
}