how to call constructor in flutter code example

Example 1: Flutter Constructor

Customer(String name, int age, String location) {
  this.name = name;
  this.age = age;
  this.location = location;
}

Customer(this.name, this.age) {
  this.name = name;
  this.age = age;
}

Example 2: constructor flutter

class Student{
  Student(int enNum){
    print(enNum);
  }
}

main(){
  var myStudent = new Student(15);
}