Java - Multiple constructors with same arguments

Question

I need to create multiple constructors with same arguments so that I can call these from my DAO class for populating different drop down values

public static Employee empType(String empCode, String empType) {

    Employee emp = new Employee();
    emp .empCode= empCode;
    emp .empType= empType;
    return emp ;
}

 public static Employee empDept(String deptCode, String deptName) {

    Employee emp = new Employee();
    emp .deptCode= deptCode;
    emp .deptName= deptName;
    return emp ;
}

When I am referencing from DAO class, how can I refer to these constructors?

E.g.

private static Employee myList(ResultSet resultSet) throws SQLException {
    return new <what should be here>((resultSet.getString("DB_NAME1")), 
                      (resultSet.getString("DB_NAME2")));
}

Even I had same type of requirements, but I don't think it is possible, since Java distinguishes overloaded method based on arguments of the methods, and if two constructor has same type of arguments, this won't work. But experts need to shed their opinion. — Pradeep Simha
– Pradeep Simha, Commented Apr 18, 2013 at 6:53
Are they really Constructors? Infact, they are not even overloaded methods! — Rahul
– Rahul, Commented Apr 18, 2013 at 6:55
@R.J you correct i thing they are two separate static methods — Rais Alam
– Rais Alam, Commented Apr 18, 2013 at 6:56
I'm amazed seeing so many responses, all talking about multiple constructors, when there aren't any in the code! — Rahul
– Rahul, Commented Apr 18, 2013 at 6:59

BobTheBuilder · Accepted Answer · 2013-04-18 06:56:05Z

11

You cant. Also, these functions aren't constructors. And how do you want to decide which "constructor" to call???

You can merge both functions:

public static Employee createEmp(String empCode, String empType, String deptName) {
    Employee emp = new Employee();
    emp .empCode= empCode;
    emp .empType= empType;
    emp .deptName= deptName;
    return emp ;
}

And use null as the unneeded argument.

answered Apr 18, 2013 at 6:56

BobTheBuilder

19.4k6 gold badges45 silver badges62 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Jacob Over a year ago

baraky null approach would be useful and better. Thanks

user5923402 Over a year ago

hi, could you give an example of using null as unneeded argument? Thanks

KyelJmD · Accepted Answer · 2013-05-10 06:13:23Z

7

You cannot Create multiple constructors/methods with the same name and same arguments

What you can do is change your implementation, and those are not Contructors.

You can follow what Baraky did, you can also use this(create a boolean flag,or an int value flag)

public Employee empType(String val1, String val2, int type) {

     Employee emp = new Employee();

    if(type == 1){
          emp .empCode= val1;
          emp .empType= val2;
    }else if(type ==2){
          emp.deptCode= val1;
          emp .deptName= val2;
     }
    return emp ;
}

edited May 10, 2013 at 6:13

answered Apr 18, 2013 at 7:00

KyelJmD

4,71210 gold badges60 silver badges79 bronze badges

3 Comments

Stian Standahl Over a year ago

if the type would be an enum the code would be more readable.

KyelJmD Over a year ago

He can also do that, or using a boolean. just pointing out that there are other approaches he or she can do.

Imrank Over a year ago

In java constructor can not be static and it can not return any value.here i think you are just overloading a function.

Sarvar Nishonboyev · Accepted Answer · 2020-03-11 09:50:01Z

From the article:

In Java you cannot have multiple methods (including constructors) with the same arguments. To get around this limitation you need to use static methods with different names that serve the client code as constructors. In the code that follows the static methods ctorApple, ctorBanana and ctorCarrot internally call the private constructor Foo() and serve in the role of multiple constructors with the same arguments. The prefix ctor is intended to remind the client that these methods serve in the role of constructors.

class Foo
{
   private Foo()
   {
     // ...
   }
   public static Foo ctorApple(/* parameters */)
   {
       Foo f = new Foo();
       // set properties here using parameters
       return f;
   }
   public static Foo ctorBanana(/* parameters */)
   {
       Foo f = new Foo();
       // set properties here using parameters
       return f;
   }
   public static Foo ctorCarrot(/* parameters */)
   {
       Foo f = new Foo();
       // set properties here using parameters
       return f;
   }
}

Stian Standahl · Accepted Answer · 2013-04-18 06:56:23Z

2

If you must have multiple constructors you could add a dummy parameter like this.

public static Employee empType(String empCode, String empType) {

    Employee emp = new Employee();
    emp .empCode= empCode;
    emp .empType= empType;
    return emp ;
}

 public static Employee empDept(String deptCode, String deptName, bool dummy) {

    Employee emp = new Employee();
    emp .deptCode= deptCode;
    emp .deptName= deptName;
    return emp ;
}

When doing this it is a minimal performance(veryveryvery small) drop, but if the code is more readable it is worth it :)

answered Apr 18, 2013 at 6:56

Stian Standahl

2,6595 gold badges37 silver badges44 bronze badges

1 Comment

Philip Over a year ago

Is this an accepted method for dealing with these kind of situations?

Alpesh Gediya · Accepted Answer · 2013-04-18 06:56:31Z

1

I do not think multiple constructor with same arguments (data type) are allowed by java.

answered Apr 18, 2013 at 6:56

Alpesh Gediya

3,8021 gold badge28 silver badges39 bronze badges

1 Comment

Rahul Over a year ago

overloaded methods?! As far as I know, overloaded methods, have the SAME NAME.

NilsH · Accepted Answer · 2013-04-18 06:58:27Z

1

If you need flexible creation of objects, check out the Builder pattern. In your case however, I don't see why it shouldn't work just to have one constructor with all your parameters. Just fetch all the properties from the resultSet, and if they're null, they'll just not be set.

answered Apr 18, 2013 at 6:58

NilsH

13.9k4 gold badges43 silver badges59 bronze badges

Comments

Vaidotas Beržinskas · Accepted Answer · 2016-05-14 17:59:53Z

1

If you have TWO same constructor with same parameter meaning but different effect, you can try to clutch them into one:

public Name(Type parameter, boolean type) {
    if(type) {

    }else {

    }
}

If you have 2+ same constructor then use int type and switch. Just suggestion.

EDIT: types in this case should be defined by enum for easier code grasp.

edited May 14, 2016 at 17:59

answered May 14, 2016 at 12:59

Vaidotas Beržinskas

5067 silver badges18 bronze badges

Comments

javakurious · Accepted Answer · 2017-06-27 17:52:53Z

1

If using a different set of parameters for the constructor changes the behavior how it acts, I would suggest extending or using composition to create a new class with the new set of parameters.

That will also adhere to OPEN/CLOSE pricipal.

answered Jun 27, 2017 at 17:52

javakurious

5271 gold badge6 silver badges14 bronze badges

Collectives™ on Stack Overflow

Java - Multiple constructors with same arguments

8 Answers 8

2 Comments

3 Comments

Comments

1 Comment

1 Comment

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

8 Answers 8

2 Comments

3 Comments

Comments

1 Comment

1 Comment

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related