There are two include statements at the start. The first line is to include a standard library stdlib.h while the second line includes the Node class file Node.cpp. This Node class is used to create nodes that form a List object. So this List factory will order Node class to create new nodes. The List class itself carries out the chain management of these Node objects. We have written our own constructor of List class as the default constructor is not sufficient enough to serve the purpose. The List constructor is parameterless. The very first step it is doing internally is that it is asking Node class to create a new node and assigning the starting address of the new Node’s object to the headNode data member. In the second statement, we are calling setNext() method of the Node class for the object pointed to by the headNode pointer. This call is to set the nextNode data member to NULL, i.e. Node’s object pointed to by the headNode pointer is not pointing to any further Node. The next statement is to set the currentNode pointer to NULL. So at the moment, we have initialized the currentNode pointer to NULL that is not pointing to any Node object. The next statement is to initialize the size data member to 0 indicating that there is no node present in the list. All this processing is done inside the constructor of List class, as we want all this done when a list object is created. Considering the analogy of car factory, the constructor function can perform certain tasks: The oil is poured into the engine, the tyres are filled-in with air etc.
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