When a class doesn't have a constructor, a default constructor is used to initialize the object with default values. Languages like Java and C# automatically provide this constructor if no custom constructors are present.
When an object is created and the class it belongs to doesn't have a constructor, most programming languages will provide a default constructor. This default constructor is a no-argument constructor that initializes the object with default values for its attributes. For instance, numerical fields might be set to zero, boolean fields might be set to false, and object references might be set to null. Some languages, like Java and C#, implicitly define this default constructor if no other constructors are explicitly defined by the programmer. This process ensures that an object has a valid state upon creation, even when no custom initialization is specified by the coder.
Using the default constructor allows for object creation and basic initialization when no explicit constructor is provided within a class, ensuring the class can still be instantiated.