What is a constructor? It's a special method, which is called during creation of an object.
Constructor looks like a method, except that name of a constructor is the same as the name of a class where it's defined and it has no return type.
You can easily generate constructors using Source -> Generate constructor.
You can have more constructors in one class and they can call themselves using keyword this.
If you don't provide your constructor, compiler will create a default constructor, which has no arguments and performs no special initialization. But if you do provide your explicit constructor, compiler won't create a default constructor.
With inheritance constructors get more interesting. You cannot inherit a constructor. And by default every constructor calls default constructor from superclass. But if you define an explicit constructor in your superclass, default constructor won't be generated, so you must call your explicit constructor on your own using super keyword.