CODEWITHSUNDEEP
inheritanceconstructordart
user350325
user350325

Reputation: 1455

Error: default constructor is already defined

In Dart, I have the following code:

class FirstClass {
  FirstClass(a) {

  }
}

class SecondClass extends FirstClass {

}

This causes and error on SecondClass because the FirstClass does not have a default constructor.

However when I try to add one.

class FirstClass {
  FirstClass(a) {

  }

  FirstClass() {

  }
}

It errors because the default constructor is already defined in FirstClass.

The only way I can seem to make this work and not error is if the superclass does not implement any constructors at all. What am I doing wrong?

Upvotes: 22

Views: 12282

Answers (2)

Jitesh Mohite
Jitesh Mohite

Reputation: 34210

In dart you cannot have multiple constructor as other language like java.

You can define default constructor as 

class FirstClass {
  FirstClass() {}
}

OR

class FirstClass {
  String name;
  int age;
  FirstClass(name, age) {
    this.name = name;
    this.age = age;
  }
}

You can not have default as well as parameter constructor in it.

Upvotes: 0

Alexandre Ardhuin
Alexandre Ardhuin

Reputation: 76213

In dart you can not have the same method/constructor name used several times (even with different parameters).

In your case you can either use named constructor to define 2 constructors :

class FirstClass {
  FirstClass() {}
  FirstClass.withA(a) {}
}

or define a as optional and keep only one constructor :

class FirstClass {
  FirstClass([a]) {}
}

Upvotes: 30

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