CODEWITHSUNDEEP
javaclassconstructor
Wells
Wells

Reputation: 23

Java beginner confused about usage of constructors

class Date {
    private int year;
    private String month;
    private int day;

    public Date() {
        month = "January";
        year = 1999;
        day = 1;
    }                                  //End of Constructor 1

    public Date(int year, String month, int day) {
        setDate(year, month, day);
    }                                  //End of Constructor 2

    public Date(int year) {
        setDate(year, "January", 1);
    }                                 //End of Constructor 3

    public void setDate(int year, String month, int day) {
        this.year = year;
        this.month = month;
        this.day = day;
    }                                //End of Constructor 4
}

public class Calendar {
    public static void main(String[] args){     
        Date date1 = new Date(2009, "March", 3);
        Date date2 = new Date(2010);
        Date date3 = new Date();
    }
}

In the code above, which constructors are called for date1, date2, and date3? How do you print the results of date1, date2, and date3 after the constructor has been called?

I tried System.out.println(date1) and so on but it gives me strange strings like u.Date@15db9742.

I was expecting to see 2009 March 1 or something of that sort.

Upvotes: 2

Views: 138

Answers (3)

Shailesh
Shailesh

Reputation: 717

you just have to match the parameters of called constructors with the defined constructors and if you are not defining any parameters then default constructor will be invoked like

Date date1 = new Date(2009, "March", 3); it will invoke 

 public Date(int year, String month, int day) {
        setDate(year, month, day);
    }                                  //End of Constructor 2

Date date3 = new Date(); will invoke

Public Date() {
        month = "January";
        year = 1999;
        day = 1;
    }                                  //End of Constructor 1

Date date2 = new Date(2010); it will invoke

public Date(int year) {
    setDate(year, "January", 1);
}                                 //End of Constructor 3

Upvotes: 0

Jimmy
Jimmy

Reputation: 2619

When you try to print object, its toString() method is called which is inherited by all java class from Object class (superclass of all java class by default). So you will have to override toString() method in your class if you need some specific contents of the object to be printed. By default, this method prints Class and its hash code. Since you have not overriden the toString(), the printed string contains object class and its hash code ( u.Date@15....). Your constructor calls are determined by the argument you pass to the constructor. Like in date1, you passed 3 parameter of type int,string and int in order. This matches your constructor 2 arguments which are of int, string and int. So in in your date1 object consturction, constructor 2 is called. similarly for date2, constructor 3 is called and for date3, default constructor i.e consturcot 1 is called.

The "constructor 4" you marked is not a constructor, it is simply a method. Constructor do not have return type.

Again , to print as you expected in your question, override toString() method in your class and format the result accordingly in that method to get expected result.

Upvotes: 2

Priyansh Goel
Priyansh Goel

Reputation: 2660

date1,date2,date3 is an object of a class Date and hence can't be printed. To print it, you will have to override toString() method.

String toString() {

 return year + " " + month + " " + day;

}

Also, Constructors are used to initialize the fields only. 

public void setDate(int year, String month, int day) {
    this.year = year;
    this.month = month;
    this.day = day;
}                                //End of Constructor 4

This method is not a constructor because the constructors always have same name as of the class and have no explicit return type.

Upvotes: 0

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