java - 如何增加下面代码中的ID值

Question

public class Student {
private String Last_Name;
private String First_Name;
private int Grade_Level, ID;
private double GPA;

public Student() {
    Last_Name = "None";
    First_Name = "None";
    Grade_Level = 0;
    GPA = 0.0;
}

public Student(String firstName, String lastName, int gradeLevel, double gpa) {
    Last_Name = lastName;
    First_Name = firstName;
    Grade_Level = gradeLevel;
    GPA = gpa;
}

public String toString(){
    return Last_Name + ", " + First_Name + "\nGPA: " + GPA + "\nGrade Level: " + Grade_Level + " id # " + ID++;
}

}

我知道每次主函数调用ID值时，它都会一次又一次地将其初始化为0，我想过使用for循环但它不起作用，所以如何解决这个问题，谢谢非常感谢您的帮助!这是示例运行:

None, None
GPA: 0.0
Grade Level: 0 id # 1

None, None
GPA: 0.0
Grade Level: 0 id # 2


None, None
GPA: 0.0
Grade Level: 0 id # 3

Dovi, Mrs.
GPA: 3.4
Grade Level: 7 id # 4

Answer 1

您可能正在寻找实例之间的共享变量，无论已创建的对象数量如何，该变量都不会更改其状态。这就是静态成员的作用:

private static int id;