超类的继承和构造函数

Question

当我在超类和子类之间放置一个箭头时，它会提示：没有找到合适的构造函数（对于超类对象。在这种情况下为 Person 中的 Date）。

构造函数和继承的故事是什么？ 为什么超类需要子类中的构造函数？

这里是超类的构造函数：

public class Date
{
    protected int _day;
    protected int _month;
    protected int _year;
    public final int MAX_DAY = 31;
    public final int MIN_DAY = 1;
    public final int MAX_MONTH = 12;
    public final int MIN_MONTH = 1;
    public final int DEFUALT_YEAR = 4;

    public Date (int day, int month, int year)
    {
      if( (MIN_DAY <= day) && (day <= MAX_DAY) && (MIN_MONTH <= month) 
      && (month <= MAX_MONTH) && (year == DEFUALT_YEAR))
      {
        this._day = day;
        this._month = month;
        this._year = year;
      }
      else
      {
        this._day = 1;
        this._month = 1;
        this._year = 2000;
      }
    }

    public Date (Date other)
    {
        _day = other._day;
        _month = other._month;
        _year = other._year; 
    } 

这里是子类的构造函数：

public class Person extends Date
{
   private String _first;
   private String _last;
   private long _id;
   private Date _date;

   public Person (String first, String last, long id, int d, int m, int y)
   {
     this._first = first;
     this._last = last;
     this._id = id;
     Date _date = new Date(d, m, y); 
    }

    public Person (Person other)
    {
     this._first = other._first;
     this._last = other._last;
     this._id = other._id;
     this._date = other._date;
    }

Answer 1

您需要调用super()以使构造函数兼容例如。

public class Person extends Date
{
   private String _first;
   private String _last;
   private long _id;
   // private Date _date; Lose the Date as every property of date is accessible here

   public Person (String first, String last, long id, int d, int m, int y)
   {
     super(d, m, y)
     this._first = first;
     this._last = last;
     this._id = id;
    }

    public Person (Person other)
    {
     this._first = other._first;
     this._last = other._last;
     this._id = other._id;
     this._day = other._day;
     this._month = other._month;
     this._year = other._year;
    }
 ...
 }

参考： https : //docs.oracle.com/javase/tutorial/java/IandI/subclasses.html

参考： https : //docs.oracle.com/javase/tutorial/java/IandI/super.html