super-constructor if there is no super class?

Question

I found a class like this:

public class Computer implements Serializable {

        private static final long serialVersionUID = 1L;    

        //...
              


        

Answer 1

By default all classes inherit java.lang.Object. So a hidden code in your class is

public class Computer extends java.lang.Object implements Serializable {

        private static final long serialVersionUID = 1L;    

        //...
        public Computer() {
            super(); //here Object's default constructor is called
        }
        //...
}

If a parent class has default constructor (no argument) and if a child class defines a default constructor, then an explicit call to parent's constructor is not necessary.

Java does it implicitly, in other words, Java puts super() before first statement of the child's constructor

consider this example

class Base {

    public Base() {
        System.out.println("base");
    }
}

class Derived extends Base {

    public Derived() {
        //super(); call is not necessary.. Java code puts it here by default
        System.out.println("derived");
    }
}

So when you create Derived d = new Derived(); the output is..

base
derived