跟踪实例化对象数量的Java类变量 [英] Java class variable that tracks number of objects instantiated

问题描述

我有一个班级Student，变量StudentID：

I have this class, Student, with the variable StudentID:

public class Student extends Person{
  int studentID = 0;
  int level;

  public Student(){

  }

  public Student(String fName, String lName, int gLevel){
    super(fName, lName);
    if(gLevel >= 0 && gLevel <= 12){
      level = gLevel;
    }
    studentID++;
  }
  public int getLevel(){
    return level;
  }
  public String toString(){
    String toReturn;
    toReturn = super.toString() + "\n   Grade Level: " + level + "\n   ID #: " + studentID;
    return toReturn;
  }
}

我希望变量StudentID继续分配创建的每个Student新的ID号。每个ID号都应比上一个创建的ID号大一个，并且应等于已创建的对象总数。现在，每个对象的ID号都分配为1。

I want the variable StudentID to keep assign each Student created a new ID number. Each ID number should be one more than the last ID number created, and so equal to the total number of objects that have been created. Right now each object is assigned the ID number of 1.

推荐答案

使StudentID成为静态成员

Make the studentID a static member

该类的每个实例中都会保留静态成员，无论有多少个clas实例。

Static members are kept throughout each instance of the class no matter how many instances of the clas there are.

   public class Student extends Person{
      static int studentID = 0;
      int level;

      public Student(){

      }

      public Student(String fName, String lName, int gLevel){
        super(fName, lName);
        if(gLevel >= 0 && gLevel <= 12){
          level = gLevel;
        }
        studentID++;
      }
      public int getLevel(){
        return level;
      }
      public String toString(){
        String toReturn;
        toReturn = super.toString() + "\n   Grade Level: " + level + "\n   ID #: " + studentID;
        return toReturn;
      }
    }

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