跟踪实例化对象数量的Java类变量

Question

我有一个带有变量StudentID的班级Student：

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继续分配给每个Student创建的新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号为1。

Answer 1

将studentID设为静态成员

静态成员将在整个类的每个实例中保留，无论有多少个clas实例。

   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;
      }
    }