Constructors

Missing default constructor

Let’s recall some facts about constructors that we covered in the previous chapter:

📝 Note

• If you do not define a constructor in your class, Java will provide a default constructor, that is, a constructor that has no parameters.
• However, if every constructor that you define has parameters, Java will not define a default constructor for you. As a consequence, invoking a constructor without arguments will be illegal.

Let’s remove the definition of the default constructor from the class Square, as given in the previous chapter. We’ll add a main method, name the resulting class Square4, and place the result in the program given below.

The class still has a constructor, so the compiler will not supply a definition of a default constructor. An attempt to invoke a default constructor will result in an error message from the compiler, as you will see when you click the RUN button.