in which situation can a constructor is used code example

Example 1: type of constructor in java

There are three types of constructors: 
Default, No-arg constructor and Parameterized.
  
If you do not implement any constructor in your class,
Java compiler inserts a default constructor into your code on your behalf.
This constructor is known as default constructor.
  
Constructor with no arguments is known as no-arg constructor

Constructor with arguments(or you can say parameters) is known as 
Parameterized constructor.

Example 2: java constructor

class Huso {
  public Huso() {
  	//constructor code about a huso
  }
}