Constructor has different parameter type with datafield

Shin Yu Wu :

I have a class called Monster, every Monster has a name, dateofbirth, and a weapon. and The Monster constructor should have the following signature:

Monster(String name, int day, int month, int year, String weaponName)

To create a monster the following code should work:

new Monster("Godzilla",11,10,2000,"VenomThrower")

So I create the datafield in Monster:

public String name;
public MyDate dateOfBirth;
public int day;
public int month;
public int year;
public Weapon weapon;

However, I have to use the MyDate class defined below to create a MyDate object for dateofbirth. And use the Weapon class defined below to create a Weapon object for the monster’s weapon.

If I have to use the Object MyDate and Weapon, their type would be different from the constructor(int day, int month, int year) and (String weaponName), I try to cast the parameters, but it compiles error. Except casting, is there another way to achieve this?? Thank you.

public class MyDate {

    private int year;
    private int month;
    private int day;


    MyDate(int year, int month, int day) {
        this.year = year;
        this.month = month;
        this.day = day;
    }

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public int getMonth() {
        return month;
    }

    public void setMonth(int month) {
        this.month = month;
    }

    public int getDay() {
        return day;
    }

    public void setDay(int day) {
        this.day = day;
    }
}

public class Weapon {

    private String name;
    Weapon(String n) {
        this.name = n;
    }
    public String getName()   {
        return name;
    }
}

Mureinik :

As you've seen, you can't just go and cast arbitrary variables to other classes. You could, however, call the respective constructors of MyDate and Weapon in Monster's constructor:

public class Monster {
    private String name;
    private MyDate dateOfBirth;
    private Weapon weapon;

    public Monster(String name, int day, int month, int year, String weaponName) {
       this.name = name;
       this.dateOfBirth = new MyDate(year, month, day);
       this.weapon = new Weapon(weaponName);
    }
}