Building a Linked List in Java Linked List

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Building a Linked List in Java

Building a Linked List in Java

Linked List • In the Procedural Paradigm a linked list consisted of: – A

Linked List • In the Procedural Paradigm a linked list consisted of: – A pointer to the head of the list – Nodes (in dynamic memory i. e. the heap) containing data and additional next pointers – Modules that would perform a variety of functions as needed: add (in order), traverse, find, delete, etc. • In the Object Oriented Paradigm a linked list will consist of a class which contains: – The head pointer (globally scoped in the class) – Methods to perform the function listed above • We will also need a class to hold the nodes. We’ll start with that. . .

Node class Node { Student. Record data; Node next; public Node(Student. Record data) {

Node class Node { Student. Record data; Node next; public Node(Student. Record data) { set. Data(data); set. Next(null); } // Constructor public void set. Data(Student. Record data) { this. data = data; // !!!!!!!!!!!!! } public void set. Next(Node next) { this. next = next; } public Student. Record get. Data() { return data; } public Node get. Next() { return next; } public String to. String() { Comments omitted if(data == null) for clarity!!! return "Node: null"; else return "Node: " + data. to. String(); }

Are we done? What about the test main? ? ?

Are we done? What about the test main? ? ?

Remember the main(e) public static void main(String args[]) { Student. Record sr = new

Remember the main(e) public static void main(String args[]) { Student. Record sr = new Student. Record("Bob", 3. 5, 123456789); Node n 1 = new Node(null); System. out. println("Empty node testn" + n 1); // Load up and print n 1. set. Data(sr); System. out. println("Bob: "+n 1); sr = new Student. Record("Mary", 3. 7, 987654321); Node n 2 = new Node(sr); n 1. set. Next(n 2); System. out. println("Bob: "+n 1); System. out. println("Mary: "+n 2); } // main } // Node

Let’s see what’s happening

Let’s see what’s happening

Tracing Student. Record sr = new Student. Record("Bob", 3. 5, 123456789); sr name =

Tracing Student. Record sr = new Student. Record("Bob", 3. 5, 123456789); sr name = "Bob" gpa = 3. 5 ssn = 123456789

Tracing Node n 1 = new Node(null); sr n 1 name = "Bob" gpa

Tracing Node n 1 = new Node(null); sr n 1 name = "Bob" gpa = 3. 5 ssn = 123456789 data next

Tracing n 1. set. Data(sr); sr n 1 name = "Bob" gpa = 3.

Tracing n 1. set. Data(sr); sr n 1 name = "Bob" gpa = 3. 5 ssn = 123456789 data next

Tracing sr = new Student. Record("Mary", 3. 7, 987654321); sr n 1 name =

Tracing sr = new Student. Record("Mary", 3. 7, 987654321); sr n 1 name = "Bob" gpa = 3. 5 ssn = 123456789 data next name = "Mary" gpa = 3. 7 ssn = 987654321

Tracing Node n 2 = new Node(sr); sr n 1 n 2 name =

Tracing Node n 2 = new Node(sr); sr n 1 n 2 name = "Bob" gpa = 3. 5 ssn = 123456789 data next name = "Mary" gpa = 3. 7 ssn = 987654321

Tracing n 1. set. Next(n 2); sr n 1 n 2 name = "Bob"

Tracing n 1. set. Next(n 2); sr n 1 n 2 name = "Bob" gpa = 3. 5 ssn = 123456789 data next name = "Mary" gpa = 3. 7 ssn = 987654321

Key to Understanding Java • Understand that the "variables" that you may think of

Key to Understanding Java • Understand that the "variables" that you may think of as objects (not primitives) are ALWAYS references (like pointers) to objects which live in the heap. • The objects live and die immobile in the heap • All the apparent movement of objects is just the moving, copying, setting-to-null of references

Review • We have created and tested two classes – class Student. Record –

Review • We have created and tested two classes – class Student. Record – class Node • We now construct the class Linked. List • We’ll start with the fields and simple accessors/modifiers • Then we’ll write the add, traverse, find and delete methods (plus helpers if necessary)

Linked. List class Linked. List { private Node head; public Linked. List() { set.

Linked. List class Linked. List { private Node head; public Linked. List() { set. Head(null); } // constructor private void set. Head(Node head) { this. head = head; } // set. Head private Node get. Head() { return head; } // get. Head

Linked. List (add method) // Purpose: add in order by SSN // Postcon: list

Linked. List (add method) // Purpose: add in order by SSN // Postcon: list will contain one additional item public void add(Student. Record sr) { if(get. Head() == null || get. Head(). get. Data(). get. Ssn() > sr. get. Ssn() ) { Node temp = new Node(sr); temp. set. Next(get. Head()); set. Head(temp); } else { add(get. Head(), sr); } } // add

Linked. List (add helper method) // Purpose: add helper private void add(Node cur, Student.

Linked. List (add helper method) // Purpose: add helper private void add(Node cur, Student. Record sr) { if( cur. get. Next() == null || cur. get. Next(). get. Data(). get. Ssn() > sr. get. Ssn() ) { Node temp = new Node(sr); temp. set. Next(cur. get. Next()); cur. set. Next(temp); } else { add(cur. get. Next(), sr); } } // add

Linked. List (traverse ) // Purpose: traverse list // Postcon: no change to list

Linked. List (traverse ) // Purpose: traverse list // Postcon: no change to list public void traverse() { traverse(get. Head()); } // traverse // Purpose: traverse helper private void traverse(Node cur) { if(cur != null) { System. out. println(cur); traverse(cur. get. Next()); } } // traverse

Linked. List (traverse ) // Purpose: print out string passed in as parameter //

Linked. List (traverse ) // Purpose: print out string passed in as parameter // then traverse list (useful for // debugging) // Postcon: No change to list public void traverse(String s) { System. out. println(s); traverse(); } // traverse

Linked. List (traverse iteratively ) // Purpose: traverse iteratively (just shown for // comparison

Linked. List (traverse iteratively ) // Purpose: traverse iteratively (just shown for // comparison // Postcon: No change to list public void traverse. I() { Node cur = get. Head(); while(cur != null) { System. out. println(cur); cur = cur. get. Next(); } } // traverse. I // Purpose: traverse iteratively with title public void traverse. I(String s) { System. out. println(s); traverse. I(); } // traverse. I

Linked. List (find ) // Purpose: Locate record by SSN // Postcon: No change

Linked. List (find ) // Purpose: Locate record by SSN // Postcon: No change to list public Student. Record find(int targ. Ssn) { return find(get. Head(), targ. Ssn); } // find // Purpose: Find helper private Student. Record find(Node cur, int targ. Ssn) { if(cur == null) return null; else if(cur. get. Data(). get. Ssn() == targ. Ssn) { return cur. get. Data(); } else { return find(cur. get. Next(), targ. Ssn); } } // find

Linked. List (delete. First)occurence // Purpose: delete first occurence of record with // matching

Linked. List (delete. First)occurence // Purpose: delete first occurence of record with // matching SSN // Postcon: If SSN found record will be removed thus // list will be one shorter public void delete. First(int targ. Ssn) { if(get. Head() != null) { if(get. Head(). get. Data(). get. Ssn() == targ. Ssn) { set. Head(get. Head(). get. Next()); } else { delete. First(get. Head(), targ. Ssn); } } } // delete. First

Linked. List (delete. First)occurence // Purpose: delete first occurence helper private void delete. First(Node

Linked. List (delete. First)occurence // Purpose: delete first occurence helper private void delete. First(Node cur, int targ. Ssn) { if(cur. get. Next() != null) { if(cur. get. Next(). get. Data(). get. Ssn() == targ. Ssn) { cur. set. Next(cur. get. Next()); } else { delete. First(cur. get. Next(), targ. Ssn); } } } // delete. First

Linked. List (delete. All)occurences // Purpose: delete all occurences matching a target // SSN

Linked. List (delete. All)occurences // Purpose: delete all occurences matching a target // SSN // Postcon: All matching occurences will be // eliminated public void delete. All(int targ. Ssn) { // (Extra Credit!!!) }

Linked. List (main) public static void main(String args[]) { Linked. List ell = new

Linked. List (main) public static void main(String args[]) { Linked. List ell = new Linked. List(); ell. traverse("Empty list traversal"); ell. add(new Student. Record("Adam", 3. 0, 333)); ell. add(new Student. Record("Bozo", 2. 0, 222)); ell. add(new Student. Record("Carl", 1. 0, 444)); ell. traverse. I("Should be 222 333 444"); ell. add(new Student. Record("Doug", 0. 0, 111)); ell. traverse("Should be 111 222 333 444"); ell. delete. First(222); ell. traverse. I("Should be 111 333 444"); ell. delete. First(999); ell. delete. First(333); ell. delete. First(111); ell. delete. First(444); ell. traverse("Empty list? ? ? "); } // main } // Linked. List

Application /* Demo application to allow user to add, find, list, * and delete

Application /* Demo application to allow user to add, find, list, * and delete student records */ class Application { // Purpose: print menu and get user choice // Postcon: returns choice as int public static int menu. Choice() { System. out. println("Enter 1 to add"); System. out. println("Enter 2 to find"); System. out. println("Enter 3 to list"); System. out. println("Enter 4 to delete"); System. out. println("Enter 5 to quit"); return IOGadget. read. Int("Choice"); }

Application // Purpose: get information to fill student record // Postcon: returns filled Student.

Application // Purpose: get information to fill student record // Postcon: returns filled Student. Record public static Student. Record get. SR() { String name = IOGadget. read. Line("Name"); double gpa = IOGadget. read. Double("GPA"); int ssn = IOGadget. read. Int("SSN"); return new Student. Record(name, gpa, ssn); }

Application // print menu and fulfill request public static void menuloop() { Linked. List

Application // print menu and fulfill request public static void menuloop() { Linked. List list = new Linked. List(); int choice; do { choice = menu. Choice(); if(choice == 1) list. add(get. SR()); else if(choice == 2) { Student. Record sr = list. find(IOGadget. read. Int("SSN")); if(sr == null) System. out. println("Not found"); else System. out. println(sr); }

Application else if(choice == 3) list. traverse("Student List"); else if(choice == 4) { int

Application else if(choice == 3) list. traverse("Student List"); else if(choice == 4) { int ssn = IOGadget. read. Int("SSN? "); list. delete. First(ssn); } else if(choice == 5) System. out. println("Exiting"); else System. out. println("Illegal choice"); } while(choice != 5); } // menuloop

Application public static void main(String args[]) { menuloop(); } } // class Application

Application public static void main(String args[]) { menuloop(); } } // class Application

Diagram class Linked. List LLNode head methods… ce tan of LLNode object Stu. Rec

Diagram class Linked. List LLNode head methods… ce tan of LLNode object Stu. Rec data LLNode next Ins ta Ins nc e of f ta n c eo Linked. List object head class LLNode Stu. Rec data LLNode next methods… Ins class Application menuloop { Linked. List list } main { menuloop() } LLNode object Stu. Rec data LLNode next