What is the constructors in class?

Answer 1

A class is simply the definition of a data type. A constructor is a special method of a class that is automatically invoked whenever an object of that type is instantiated, and is used to initialise the object's data members.

Answer 2

The constructors in a java class are the methods set up to instantiate, or create an instance of the class. Often, a constructor will accept parameters to add information to the object that will be created. Here is an example:

public class Person

{

String name;

int age;

char gender;

public Person(String n, int a, char g)

{

this.name=n;

this.age=a;

this.gender=g;

}

public Person(String n)

{

this.name=n;

this.age=18;

this.gender='m';

}

}

In this example, the two methods in boldface are constructors. In another program they could be called, and an instance of the class would be created. The reason there can be more than one constrcutor( and i could have made only one) is that they take different parameters. The first one creates an object of type Person with 3 variables: age, name and gender. These three variables are all set by the constructor. The second constructor allows an instance to be created with only the name known. It sets the name to whatever value was specified as a parameter, and it sets the age to the default value of 18 and the gender to 'm'. Another program could look like this:

public class MakeAName

{

public static void main(String[] args)

{

Person joelle = new Person("Joelle", 15, 'f');

Person Tim = new Person("Tim");

}

}

This program, if it was in the same folder as the Person class file, would create two objects (variables). the first would be joelle, which would be an object of type Person with name "Joelle", age 15, and gender 'f.' The second would be Tim, which would be an object of type Person, with name "Tim". It would have age 25, and gender 'm', because in the constructor i only listed a String value ("Tim"), but no int or char values. therefore, the program would know to run the constructor that accepted only a String value (the second constructor). This constructor set the age to 25 and the gender to 'm'. remember? anyway, another thing is that you cannot call a constructor with a different number or type of variables than already specified. So I could not have said in the second program :

Person Jim = new Person("Jim", 34).

This is because i never made a constructor that was declared as such:

public Person(String s, int i)

{

//put code here

}

And my final point i would like to say is that, if a class (that is not a static class, which means it cannot have a constructor, but this is more advanced stuff) does not contain a constructor at all, it can still be instantiated. For example, if there was a class called Animal, but it did not have a constructor in it, it could still be instantiated as such:

Animal a = new Animal();

This would create the Object (or variable) a which has the type Animal. However, it does NOT contain any personalized data as the Person class did (name, age, and gender)

So that is what a constructor is. Hope it helped!!!!

Answer 3

Class constructor is a structure within class definition that serves to create and/or initialize variable defined within class.