Constructors in Java are special methods that are used to initialize objects when they are created. They have the same name as the class and no return type. When an object is created, the constructor is called automatically, and it can be used to set initial values for object attributes. If a class does not have a constructor, Java creates a default constructor automatically, which initializes instance variables with default values.

Constructors can also take parameters, which are used to initialize attributes. There are three types of constructors in Java: no-arg constructor, parameterized constructor, and default constructor. The no-arg constructor does not accept any arguments, the parameterized constructor accepts arguments, and the default constructor is automatically created by Java if a class does not have a constructor.

In summary, constructors in Java are used to initialize objects when they are created, and they have the same name as the class and no return type. They can be used to set initial values for object attributes and can take parameters to initialize attributes. If a class does not have a constructor, Java creates a default constructor automatically.