linked structures list figure provides an example of linked list consisting of five nodes the last node in the listcommonly called the tail nodeis indicated by null link reference most nodes in the list have no name and are simply referenced via the link field of the preceding node the first node in the listhowevermust be named or referenced by an external variable as it provides an entry point into the linked list this variable is commonly known as the head pointeror head reference linked list can also be emptywhich is indicated when the head reference is null head figure singly linked list consisting of five nodes and head reference linked structures are built using fundamental components provided by the programming languagenamely reference variables and objects the linked list is just one of several linked structures that we can create if more links are added to each nodeas illustrated in figure we can connect the nodes to form any type of configuration we may need the tree structurewhich organizes the nodes in hierarchical fashionis another commonly used linked structure that we explore later in and entry figure an example of complex linked structure linked list is data structure that can be used to implement any number of abstract data types while some languages do provideas part of their standard librarya generic list adt implemented using linked listwe are going to create and work with linked lists directly some algorithms and abstract data types can be implemented more efficiently if we have direct access to the individual nodes within the adt than would be possible if we created generic linked list class