java - 在JAVA中创建一个方法来调用另一个类的特定格式来打印ArrayList的内容

Question

在此示例中，我想将一所学校的学生添加到 ArrayList 中，并通过另一个类中定义的另一个方法以多态格式打印数组列表。

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 
    }
}

输出应该是这样的:

  Sam, Male, 13
  John, Male, 11
  Elle, Female, 12
  Paul, Male, 12
  Javinia, Female, 11
  Paperino, Male, 12

我是 JAVA 新手，不知道该怎么做。看起来似乎很容易。我为性别创建了两个类，因为稍后可以轻松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。

感谢您抽出时间并提供帮助。

Answer 1

一般来说，我们通过覆盖toString()来做到这一点某个类的方法，然后打印它。

将以下内容视为建设性批评:这里存在很多问题。

1. 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。并不是每个学生都会有相同的经历例如，姓名。
2. 同样，您也不会调用 Student.function() ，您可以调用this.function()只称呼该学生，而不是类(class)学生。 this是 Student 的一个实例。
3. 你绝对不想做ArrayList<Student> students = new
ArrayList<Student>();在你的 addStudent() 方法中。你是每次添加学生时都会重置学生列表。保持在类级别声明中或者更好的是，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()); 
    }
}