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Ch04 Linked List Structure
 

Ch04 Linked List Structure

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    Ch04 Linked List Structure Ch04 Linked List Structure Presentation Transcript

    • Chapter 4 Linked Structures
    • Chapter Objectives
      • Describe the use of references to create linked structures
      • Compare linked structures to array-based structures
      • Explore the techniques for managing a linked list
      • Discuss the need for a separate node to form linked structures
      • Implement a set collection using a linked list
    • References as Links
      • There are many ways to implement a collection
      • In chapter 3 we explored an array-based implementation of a set collection
      • A linked structure uses object reference variables to link one object to another
      • Recall that an object reference variable stores the address of an object
      • In that sense, an object reference is a pointer to an object
    • FIGURE 4.1 An object reference variable pointing to an object
    • Self-Referential Objects
      • A Person object, for instance, could contain a reference variable to another Person object:
      public class Person { private String name; private String address; private Person next; // a link to another Person object // whatever else }
    • Linked Lists
      • This type of reference can be used to form a linked list , in which one object refers to the next, which refers to the next, etc.
      • Each object in a list is often generically called a node
      • A linked list is a dynamic data structure in that its size grows and shrinks as needed, unlike an array, whose size is fixed
      • Java objects are created dynamically when they are instantiated
    • FIGURE 4.2 A linked list
    • Non-linear Structures
      • A linked list, as the name implies, is a linear structure
      • Object references also allow us to create non-linear structures such as hierarchies and graphs
    • FIGURE 4.3 A complex linked structure
    • Managing Linked Lists
      • The references in a linked list must be carefully managed to maintain the integrity of the structure
      • Special care must be taken to ensure that the entry point into the list is maintained properly
      • The order in which certain steps are taken is important
      • Consider inserting and deleting nodes in various positions within the list
    • FIGURE 4.4 Inserting a node at the front of a linked list
    • FIGURE 4.5 Inserting a node in the middle of a linked list
    • FIGURE 4.6 Deleting the first node in a linked list
    • FIGURE 4.7 Deleting an interior node from a linked list
    • Elements without Links
      • The problem with self-referential objects is that they "know" they are part of a list
      • A better approach is to manage a separate list of nodes that also reference the objects stored in the list
      • The list is still managed using the same techniques
      • The objects stored in the list need no special implementation to be part of the list
      • A generic list collection can be used to store any kind of object
    • FIGURE 4.8 Using separate node objects to store and link elements
    • Doubly Linked Lists
      • There are variations on the implementation of linked lists that may be useful in particular situations
      • For example, in a doubly linked list each node has a reference to both the next and previous nodes in the list
      • This makes traversing the list easier
    • FIGURE 4.9 A doubly linked list
    • Listing 4.1
    • Listing 4.1 (cont.)
    • Listing 4.1 (cont.)
    • FIGURE 4.10 A linked implementation of a set collection
    • LinkedSet - Constructor
    • LinkedSet - the add Operation
    • LinkedSet - the removeRandom Operation
    • LinkedSet - the removeRandom Operation
    • LinkedSet - the remove Operation
    • LinkedSet - the remove Operation
    • LinkedSet - the remove Operation
    • LinkedSet - the iterator Operation
    • Listing 4.2
    • Listing 4.2 (cont.)
    • Listing 4.2 (cont.)
    • FIGURE 4.11 UML description of the LinkedSet<T> class
    • Analysis of Linked Operations
      • Since the order is irrelevant, and there is no capacity to expand, adding an element to the set is O(1)
      • Removing a particular element, because it must be found, is O(n)
      • Removing a random element requires a traversal of the list, and therefore is O(n)