what does a default constructor do code example

Example: default constructor

public class Vehicle {
  protected String vin;
  protected int modelYear;
  
  public Vehicle() { } 
  
  public Vehicle(String vin) { 
    this.vin = vin;
  }
   
  public Vehicle(String vin, int modelYear) { 
    this.vin = vin;
    this.modelYear = modelYear;
  }
}