vault backup: 2024-03-05 16:01:50

.obsidian/workspace.json

@@ -8,12 +8,12 @@
         "type": "tabs",
         "children": [
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-            "id": "90e6fc52439b47f9",
+            "id": "e96e468fb0a709e5",
             "type": "leaf",
             "state": {
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               "state": {
-                "file": "Semester 2/Database Systems/Week 7/Week 7 Database Systems.md",
+                "file": "Semester 2/Database Systems/Week 8/Week 8 Database Systems.md",
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               }
@@ -30,21 +30,11 @@
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         "type": "tabs",
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@@ -53,8 +43,7 @@
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-        "currentTab": 1
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     "direction": "vertical"
@@ -121,7 +110,7 @@
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               "state": {
-                "file": "Semester 2/Database Systems/Booklet of Lecture Slides for Semester Two (2).pdf",
+                "file": "Semester 2/Database Systems/Week 8/Week 8 Database Systems.md",
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                 "sortOrder": "alphabetical",
@@ -138,7 +127,7 @@
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-                "file": "Semester 2/Database Systems/Booklet of Lecture Slides for Semester Two (2).pdf",
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@@ -161,7 +150,7 @@
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@@ -203,34 +192,36 @@
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     "Semester 2/Programming 2/Project/Part 2/Periodical.java#",
     "Semester 2/Programming 2/Project/Part 2/LibraryItem.java#",
+    "Semester 2/Programming 2/Project/Part 2/LibraryUser.java#",
+    "Semester 2/Programming 2/Project/Part 2/CD.java#",
+    "Semester 2/Programming 2/Project/Part 2/DVD.java#",
+    "Semester 2/Programming 2/Project/Part 2/AudioVisual.java#",
+    "Semester 2/Programming 2/Project/Part 2/PrintedItem.java#",
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     "Semester 2/Computer Systems Internals & Linux/Week 6/Week 6 Computer Systems Internals.md",
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-    "Semester 2/Computer Systems Internals & Linux/Week 6",
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     "Semester 2/Programming 2/Assessment 3 Revision/Parameter Passing WS1.md",
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@@ -247,7 +238,6 @@
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     "Semester 2/Database Systems/Week 2/Week 2 Database Systems.md",
     "CCNA/1 - Networking Today/1.2 - Network Components.md",
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Semester 2/Database Systems/Week 8/Week 8 Database Systems.md

@@ -0,0 +1,90 @@
+# [Undoing & Redoing Transactions](Semester%202/Database%20Systems/Week%207/Week%207%20Database%20Systems.md####Undoing%20Transactions)
+
+# Deferred Update Protocol
+
+Updates not written until after transaction has reached commit point.
+If transaction fails before committing, no modification is made to database, hence no undoing is required.
+May be necessary to redo updates of committed transactions as effect may not have reached database.
+
+## Procedure
+
+Redo transaction is both \<T1 start> and \<T1 commit> are present in the log
+
+### Example
+
+![](Pasted%20image%2020240305130824.png)
+Failure in different places:
+![](Pasted%20image%2020240305131110.png)
+In case(a), no commit is present, so no redo or undo is required.
+case(b), T0 commits, but T1 does not, hence T0 is redone.
+case(b), T0 and T1 commits, so both are redone.
+
+# Immediate Update Protocol
+
+Updates applied as they occur.
+Following a failure, redo updates of committed transactions.
+Undo effects of transactions uncommitted.
+If no commit record, transacation was active and must be undone.
+Undo operations performed in reverse order in log.
+In recovery, use log to undo or redo.
+
+## Protocol
+
+Undo
+
+- If <Ti,start> is in the log but <Ti,commit> is not then restore the value of all data items updated by Ti to their old values, going backwards from the last log record for Ti.
+Redo
+- If <Ti,start> and <Ti,commit> are both in the log then set the value of all data items updated by Ti to the new values, going forward from the first log record for Ti
+
+### Example
+
+![](Pasted%20image%2020240305134506.png)
+
+# Checkpoints
+
+After failure, may not know how far back to search log.
+Checkpoints limit log searching, made automatically by DBMS
+Creation of checkpoints schedules at predetermined intervals.
+Definition: Checkpoints are points of sync between database and log file. All buffers are written to secondary storage.
+
+## Procedure
+
+1. Write to secondary storage
+	- All log records
+	- All modified buffer blocks to database.
+	- Checkpoint record to log file which contains identities of transactions active at time of checkpoint
+2. Resume processing.
+
+![](Pasted%20image%2020240305134734.png)
+
+### Example 1 ( Immediate )
+
+- Starts at t0, fails at tf.
+- T1 and T6 have to be undone
+- In absence of other info, recovery manager has to redo T2, 3, 4, and 5.
+- ![](Pasted%20image%2020240305134835.png)
+### Example 2 ( serial with checkpoint, Immediate )
+
+- Dotted lines = checkpoints
+- T1 is safe since updates are written to disk
+- T4 needs to be undone
+- T2 and 3 need to be redone
+- ![](Pasted%20image%2020240305134944.png)
+### Example 3 ( concurrent with checkpoint, Immediate )
+
+- T2 and 3 safe since written to disk
+- T1 and 6 need to be undone.
+- Since checkpoint, redo T4 and 5.
+- ![](Pasted%20image%2020240305135043.png)
+# Purpose of Recovery Log File
+
+- Scan log backwards
+- Create undo / redo lists
+- Undo List: Transactions active at time of crash
+	- Perform undo(T) for every transaction in list
+	- Stop when reaching \<T, start> for every transaction in list.
+- Redo List: Transactions committed after last checkpoint
+	- Redo for each transaction in list.
+
+## Example of Log Use ( Immediate )
+![](Pasted%20image%2020240305135229.png)

Semester 2/Programming 2/Project/Part 2/AudioVisual.java

@@ -1,14 +1,12 @@
 
 /**
- * Write a description of class AudioVisual here.
+ * Subclass of LibraryItem to create objects of audio and visual items in a library.
  * 
- * @author (your name) 
+ * @George Wilkinson
- * @version (a version number or a date)
+ * @1.0
  */
 
 import java.util.Scanner;
-import java.util.ArrayList;
-import java.util.NoSuchElementException;
 
 public abstract class AudioVisual extends LibraryItem
 {

Semester 2/Programming 2/Project/Part 2/Book.ctxt

@@ -1,9 +1,23 @@
 #BlueJ class context
 comment0.params=
 comment0.target=Book()
-comment0.text=\n\ Constructor\ for\ objects\ of\ class\ Book\n
+comment0.text=\n\ Constructor\ for\ objects\ of\ class\ Book\n\ Since\ all\ field\ variables\ initialise\ as\ null,\ nothing\ should\ happen\ here.\n
 comment1.params=
-comment1.target=void\ printDetails()
+comment1.target=java.lang.String\ getAuthor()
-comment2.params=detailScanner
+comment1.text=\n\ Return\ value\ of\ @author\n
-comment2.target=void\ readItemData(java.util.Scanner)
+comment2.params=
-numComments=3
+comment2.target=java.lang.String\ getIsbn()
+comment2.text=\n\ Return\ value\ of\ @isbn.\n
+comment3.params=author
+comment3.target=void\ setAuthor(java.lang.String)
+comment3.text=\n\ Set\ value\ of\ @author.\n
+comment4.params=isbn
+comment4.target=void\ setIsbn(java.lang.String)
+comment4.text=\n\ Set\ value\ of\ @isbn\n
+comment5.params=
+comment5.target=void\ printDetails()
+comment5.text=\n\ Print\ to\ terminal,\ relevant\ details\ of\ current\ object.\n
+comment6.params=detailScanner
+comment6.target=void\ readItemData(java.util.Scanner)
+comment6.text=\n\ Passed\ a\ scanner\ object,\ set\ field\ variables\ to\ corresponding\ values.\n
+numComments=7

Semester 2/Programming 2/Project/Part 2/Book.java

@@ -3,7 +3,7 @@
  * Subclass of LibraryItem that emulates a Book item.
  * 
  * @George Wilkinson 
- * @1.0
+ * @2.3
  */
 
 import java.util.Scanner;
@@ -15,15 +15,54 @@ public class Book extends PrintedItem
 
     /**
      * Constructor for objects of class Book
+     * Since all field variables initialise as null, nothing should happen here.
      */
     public Book(){}
     
+    /*
+     * Return value of @author
+     */
+    public String getAuthor()
+    {
+        return author;
+    }
+    
+    /*
+     * Return value of @isbn.
+     */
+    public String getIsbn()
+    {
+        return isbn;
+    }
+    
+    /*
+     * Set value of @author.
+     */
+    public void setAuthor( String author )
+    {
+        this.author = author;
+    }
+    
+    /*
+     * Set value of @isbn
+     */
+    public void setIsbn( String isbn )
+    {
+        this.isbn = isbn;
+    }
+    
+    /*
+     * Print to terminal, relevant details of current object.
+     */
     public void printDetails() {
         System.out.println( "ISBN: " + isbn +
         "\nAuthor: " + author );
         super.printDetails();
     }
     
+    /*
+     * Passed a scanner object, set field variables to corresponding values.
+     */
     public void readItemData( Scanner detailScanner ){
         if ( detailScanner != null ) {
             this.author = detailScanner.next().trim();

Semester 2/Programming 2/Project/Part 2/CD.ctxt

@@ -1,17 +1,23 @@
 #BlueJ class context
 comment0.params=
 comment0.target=CD()
-comment0.text=\n\ Constructor\ for\ objects\ of\ class\ CD\n
+comment0.text=\n\ Constructor\ for\ objects\ of\ class\ CD\n\ Since\ all\ field\ variables\ initialise\ as\ null,\ nothing\ should\ happen\ here.\n
 comment1.params=
 comment1.target=java.lang.String\ getArtist()
+comment1.text=\n\ Return\ value\ of\ @artist.\n
 comment2.params=
 comment2.target=int\ noOfTracks()
+comment2.text=\n\ Return\ value\ of\ @noOfTracks\n
 comment3.params=artist
 comment3.target=void\ setArtist(java.lang.String)
+comment3.text=\n\ Set\ value\ of\ @artist.\n
 comment4.params=noOfTracks
 comment4.target=void\ setNoOfTracks(int)
+comment4.text=\n\ Set\ value\ of\ @noOfTracks.\n
 comment5.params=
 comment5.target=void\ printDetails()
+comment5.text=\n\ Print\ to\ terminal,\ relevant\ details\ of\ current\ object.\n
 comment6.params=detailScanner
 comment6.target=void\ readItemData(java.util.Scanner)
+comment6.text=\n\ Passed\ a\ scanner,\ set\ the\ relevant\ details\ to\ their\ corresponding\ field\ variables.\n
 numComments=7

Semester 2/Programming 2/Project/Part 2/CD.java

@@ -1,9 +1,9 @@
 
 /**
- * Write a description of class CD here.
+ * Subclass of AudioVisual, to create objects of a CD.
  * 
- * @author (your name) 
+ * @George Wilkinson
- * @version (a version number or a date)
+ * @1.0
  */
 
 import java.util.Scanner;
@@ -15,35 +15,54 @@ public class CD extends AudioVisual
     
     /**
      * Constructor for objects of class CD
+     * Since all field variables initialise as null, nothing should happen here.
      */
     public CD(){}
     
+    /*
+     * Return value of @artist.
+     */
     public String getArtist()
     {
         return artist;
     }
     
+    /*
+     * Return value of @noOfTracks
+     */
     public int noOfTracks()
     {
         return noOfTracks;
     }
     
+    /*
+     * Set value of @artist.
+     */
     public void setArtist( String artist )
     {
         this.artist = artist;
     }
     
+    /*
+     * Set value of @noOfTracks.
+     */
     public void setNoOfTracks( int noOfTracks )
     {
         this.noOfTracks = noOfTracks;
     }
     
+    /*
+     * Print to terminal, relevant details of current object.
+     */
     public void printDetails() {
         System.out.println( "Artist: " + artist +
         "\nTrack Count: " + noOfTracks );
         super.printDetails();
     }
     
+    /*
+     * Passed a scanner, set the relevant details to their corresponding field variables.
+     */
     public void readItemData( Scanner detailScanner ){
         if ( detailScanner != null ) {
             this.artist = detailScanner.next().trim();

Semester 2/Programming 2/Project/Part 2/DVD.ctxt

@@ -1,13 +1,17 @@
 #BlueJ class context
 comment0.params=
 comment0.target=DVD()
-comment0.text=\n\ Constructor\ for\ objects\ of\ class\ DVD\n
+comment0.text=\n\ Constructor\ for\ objects\ of\ class\ DVD\n\ Since\ all\ field\ variables\ initialise\ as\ null,\ nothing\ should\ happen\ here.\n
 comment1.params=
 comment1.target=java.lang.String\ getDirector()
+comment1.text=\n\ Return\ value\ of\ @director.\n
 comment2.params=director
 comment2.target=void\ setDirector(java.lang.String)
+comment2.text=\n\ Set\ value\ of\ @director.\n
 comment3.params=
 comment3.target=void\ printDetails()
+comment3.text=\n\ Print\ relevant\ details\ of\ the\ current\ object.\n
 comment4.params=detailScanner
 comment4.target=void\ readItemData(java.util.Scanner)
+comment4.text=\n\ Passed\ a\ scanner\ object,\ give\ the\ relevant\ variable\ a\ value.\n
 numComments=5

Semester 2/Programming 2/Project/Part 2/DVD.java

@@ -1,9 +1,9 @@
 
 /**
- * Write a description of class DVD here.
+ * Subclass of AudioVisual to create objects of DVD items.
  * 
- * @author (your name) 
+ * @George Wilkinson
- * @version (a version number or a date)
+ * @1.0
  */
 
 import java.util.Scanner;
@@ -11,26 +11,40 @@ import java.util.Scanner;
 public class DVD extends AudioVisual
 {
     private String director;
+    
     /**
      * Constructor for objects of class DVD
+     * Since all field variables initialise as null, nothing should happen here.
      */
     public DVD(){}
     
+    /*
+     * Return value of @director.
+     */
     public String getDirector()
     {
         return director;
     }
     
+    /*
+     * Set value of @director.
+     */
     public void setDirector( String director )
     {
         this.director = director;
     }
     
+    /*
+     * Print relevant details of the current object.
+     */
     public void printDetails() {
         System.out.println( "Director: " + director );
         super.printDetails();
     }
     
+    /*
+     * Passed a scanner object, give the relevant variable a value.
+     */
     public void readItemData( Scanner detailScanner ){
         if ( detailScanner != null ) {
             this.director = detailScanner.next().trim();

Semester 2/Programming 2/Project/Part 2/Library.ctxt

@@ -10,7 +10,7 @@ comment2.target=void\ storeUser(LibraryUser)
 comment2.text=\n\ Appends\ a\ LibraryUser\ to\ the\ userList.\n
 comment3.params=prefix\ length
 comment3.target=java.lang.String\ generateUserID(java.lang.String,\ int)
-comment3.text=\n\ Returns\ a\ random\ unique\ user\ ID\ by\ specifying\ \n\ @prefix\ -\ arbitrary\ alphanumeric\ prefix\n\ @length\ -\ length\ of\ numeric\ ID\n\ \n\ Example\:\ length\ \=\ 6,\ expected\ result\ should\ be\ under\ 999,999\ and\ above\ 99,999.\n\ If\ we\ just\ use\ 10^(length),\ this\ would\ generate\ any\ number\ under\ 1,000,000.\n\ This\ is\ an\ issue\ since\ any\ integers\ below\ 100,000\ can\ be\ used,\ which\ would\ be\ incorrect.\n\ By\ using\ the\ offset\ of\ a\ factor\ of\ 10\ below\ the\ desired\ length\ we\ can\ generate\ between\ 0\ and\ 899,999.\n\ After\ this,\ we\ can\ add\ 100,000\ back\ to\ the\ number\ to\ ensure\ a\ baseline\ length\ is\ maintained.\n\ \n\ Note\:\ I\ am\ aware\ that\ this\ is\ overengineered,\ and\ that\ several\ random\ integers\ of\ amount\ @length\ could\ be\ used,\ \n\ but\ this\ is\ considerably\ more\ efficient\ since\ there\ is\ no\ iteration\ involved\ in\ the\ creation\ of\ the\ ID.\ O(1)\n
+comment3.text=\n\ Returns\ a\ random\ unique\ user\ ID\ by\ specifying\ \n\ @prefix\ -\ arbitrary\ alphanumeric\ prefix\n\ @length\ -\ length\ of\ numeric\ ID\n\ and\ returning\ a\ unique\ user\ id\n\ @uuid\ -\ a\ unique\ string\ starting\ with\ @prefix,\ and\ concat.\ with\ a\ random\ number\n\ \n\ Example\:\ length\ \=\ 6,\ expected\ result\ should\ be\ under\ 999,999\ and\ above\ 99,999.\n\ If\ we\ just\ use\ 10^(length),\ this\ would\ generate\ any\ number\ under\ 1,000,000.\n\ This\ is\ an\ issue\ since\ any\ integers\ below\ 100,000\ can\ be\ used,\ which\ would\ be\ incorrect.\n\ By\ using\ the\ offset\ of\ a\ factor\ of\ 10\ below\ the\ desired\ length\ we\ can\ generate\ between\ 0\ and\ 899,999.\n\ After\ this,\ we\ can\ add\ 100,000\ back\ to\ the\ number\ to\ ensure\ a\ baseline\ length\ is\ maintained.\n\ \n\ Note\:\ I\ am\ aware\ that\ this\ is\ overengineered,\ and\ that\ several\ random\ integers\ of\ amount\ @length\ could\ be\ used,\ \n\ but\ this\ is\ considerably\ more\ efficient\ since\ there\ is\ no\ iteration\ involved\ in\ the\ creation\ of\ the\ ID.\ O(1)\n
 comment4.params=
 comment4.target=void\ writeUserData()
 comment4.text=\n\ A\ method\ to\ output\ all\ user\ data\ to\ a\ file\ using\ a\ fileDialog\ to\ specify\ file\ location.\n\ \n\ Note\:\ Potentially\ could\ implement\ the\ HashSet\ made\ for\ GenerateUserID\ to\ avoid\ unnecessary\ recursion.\n

Semester 2/Programming 2/Project/Part 2/Library.java

@@ -3,7 +3,7 @@
  * Class to create objects of a Library, which can hold and report on assets held within
  * 
  * @George Wilkinson
- * @2.0
+ * @3.0
  */
 
 // Import all required libraries. Not using .* as it is not good practice due to potential conflicts.

Semester 2/Programming 2/Project/Part 2/LibraryItem.ctxt

@@ -6,9 +6,10 @@ comment1.params=
 comment1.target=java.lang.String\ getItemCode()
 comment10.params=
 comment10.target=void\ printDetails()
-comment10.text=\n\ \ \ \ public\ void\ printDetails()\n\ \ \ \ {\n\ \ \ \ \ \ \ \ System.out.println(\ title\ +\ "\ with\ an\ item\ code\ "\ +\ itemCode\ +\ "\ has\ been\ borrowed\ "\ +\ timesBorrowed\ +\ "\ times.");\n\ \ \ \ \ \ \ \ if(\ onLoan\ )\n\ \ \ \ \ \ \ \ \ \ \ \ System.out.println(\ "This\ item\ is\ at\ present\ on\ loan\ and\ when\ new\ cost\ "\ +\ cost\ +\ "\ pence.\\n"\ );\n\ \ \ \ \ \ \ \ else\ \n\ \ \ \ \ \ \ \ \ \ \ \ System.out.println(\ "This\ item\ is\ at\ present\ not\ on\ loan\ and\ when\ new\ cost\ "\ +\ cost\ +\ "\ pence.\\n"\ );\n\ \ \ \ }\n
+comment10.text=\n\ Print\ to\ terminal,\ relevant\ field\ variables\n
 comment11.params=detailScanner
 comment11.target=void\ readItemData(java.util.Scanner)
+comment11.text=\n\ Passed\ a\ scanner\ object,\ assign\ values\ to\ relevant\ field\ variables\n
 comment2.params=
 comment2.target=int\ getCost()
 comment3.params=

Semester 2/Programming 2/Project/Part 2/LibraryItem.java

@@ -3,7 +3,7 @@
  * Superclass of items / assets stored in a Library.
  * 
  * @George Wilkinson
- * @2.1
+ * @3.1
  */
 
 import java.util.Scanner;
@@ -12,7 +12,7 @@ import java.util.NoSuchElementException;
 
 public abstract class LibraryItem
 {
-    // instance variables - replace the example below with your own
+    // instance variables
     private String title;
     private String itemCode;
     private int cost;
@@ -82,24 +82,14 @@ public abstract class LibraryItem
      * Field Mutator End
      */
    
-    // Output to console the details of the fields in a human-readable format. 
+   /*
-    
+    * Print to terminal, relevant field variables
-    /*
-    public void printDetails()
-    {
-        System.out.println( title + " with an item code " + itemCode + " has been borrowed " + timesBorrowed + " times.");
-        if( onLoan )
-            System.out.println( "This item is at present on loan and when new cost " + cost + " pence.\n" );
-        else 
-            System.out.println( "This item is at present not on loan and when new cost " + cost + " pence.\n" );
-    }
     */
-    
    public void printDetails()
    {
         System.out.println("Item Code: " + itemCode +
         "\nTitle: " + title +
-        "\nCost: £" + ( ( float )( cost ) )/100 +
+        "\nCost: £" + ( ( float )( cost ) )/100 + // Convert cost in pence to £pounds.pence to be more readable.
         "\nBorrowed " + getTimesBorrowed() + " times." );
         if( getOnLoan() )
             System.out.println( "On Loan");
@@ -107,6 +97,9 @@ public abstract class LibraryItem
             System.out.println( "Available to Loan");
    }
    
+   /*
+    * Passed a scanner object, assign values to relevant field variables
+    */
    public void readItemData( Scanner detailScanner ) {
         
         if ( detailScanner != null ) {

Semester 2/Programming 2/Project/Part 2/LibraryUser.ctxt

@@ -4,14 +4,18 @@ comment0.target=LibraryUser()
 comment0.text=\n\ Constructor\ for\ objects\ of\ class\ LibraryUser\n
 comment1.params=
 comment1.target=java.lang.String\ getUserID()
+comment1.text=\n\ Accessor\ start\ -\ return\ values\ of\ corresponding\ variables.\n
 comment10.params=title
 comment10.target=void\ setTitle(java.lang.String)
 comment11.params=writer
 comment11.target=void\ writeData(java.io.PrintWriter)
+comment11.text=\n\ Passed\ a\ PrintWriter,\ append\ field\ variables\ in\ a\ set\ format,\ and\ flush\ the\ buffer.\n
 comment12.params=
 comment12.target=void\ printDetails()
+comment12.text=\n\ Print\ to\ terminal,\ all\ relevant\ fields.\n
 comment13.params=detailScanner
 comment13.target=void\ readData(java.util.Scanner)
+comment13.text=\n\ Passed\ a\ scanner\ object,\ assign\ relevant\ values\ to\ field\ variables.\n
 comment2.params=
 comment2.target=java.lang.String\ getSurname()
 comment3.params=
@@ -22,6 +26,7 @@ comment5.params=
 comment5.target=java.lang.String\ getTitle()
 comment6.params=userID
 comment6.target=void\ setUserID(java.lang.String)
+comment6.text=\n\ Accessor\ End\n\ Mutator\ Start\ -\ Set\ value\ of\ corresponding\ variables\n
 comment7.params=surname
 comment7.target=void\ setSurname(java.lang.String)
 comment8.params=firstName

Semester 2/Programming 2/Project/Part 2/LibraryUser.java

@@ -1,9 +1,9 @@
 
 /**
- * Write a description of class LibraryUser here.
+ * Class LibraryUser to create a user of a library.
  * 
- * @author (your name) 
+ * @George Wilkinson
- * @version (a version number or a date)
+ * @1.0
  */
 
 import java.util.Scanner;
@@ -11,7 +11,7 @@ import java.io.PrintWriter;
 
 public class LibraryUser
 {
-    // instance variables - replace the example below with your own
+    // instance variables
     private String userID, surname, firstName, otherInitials, title;
 
     /**
@@ -19,6 +19,9 @@ public class LibraryUser
      */
     public LibraryUser(){}
 
+    /*
+     * Accessor start - return values of corresponding variables.
+     */
     public String getUserID(){
         return userID;
     }
@@ -39,7 +42,10 @@ public class LibraryUser
         return title;
     }
     
-    
+    /*
+     * Accessor End
+     * Mutator Start - Set value of corresponding variables
+     */
    
     public void setUserID( String userID ){
         this.userID = userID;
@@ -61,18 +67,31 @@ public class LibraryUser
         this.title = title;
     }
     
+    /*
+     * Mutator End
+     */
+    
+    /*
+     * Passed a PrintWriter, append field variables in a set format, and flush the buffer.
+     */
     public void writeData( PrintWriter writer ) 
     {
         writer.print(userID + ", " + surname + ", " + firstName + ", " + otherInitials + ", " + title + "\n");
         writer.flush();
     }
     
+    /*
+     * Print to terminal, all relevant fields.
+     */
     public void printDetails()
     {
         System.out.println( "ID: " + userID +
         "\nName: " + title + " " + firstName + " " + otherInitials + " " + surname );
     }
     
+    /*
+     * Passed a scanner object, assign relevant values to field variables.
+     */
     public void readData( Scanner detailScanner )
     {
         if ( detailScanner != null ) {

Semester 2/Programming 2/Project/Part 2/Periodical.ctxt

@@ -1,8 +1,17 @@
 #BlueJ class context
 comment0.params=
 comment0.target=Periodical()
+comment0.text=\n\ Constructor\ for\ objects\ of\ class\ Periodical\n\ Since\ all\ field\ variables\ initialise\ as\ null,\ nothing\ should\ happen\ here.\n
 comment1.params=
-comment1.target=void\ printDetails()
+comment1.target=java.lang.String\ getPublicationDate()
-comment2.params=detailScanner
+comment1.text=\n\ Return\ value\ of\ @publicationDate\n
-comment2.target=void\ readItemData(java.util.Scanner)
+comment2.params=publicationDate
-numComments=3
+comment2.target=void\ setPublicationDate(java.lang.String)
+comment2.text=\n\ Set\ value\ of\ @publicationDate\n
+comment3.params=
+comment3.target=void\ printDetails()
+comment3.text=\n\ Print\ to\ terminal,\ relevant\ field\ variable's\ values.\n
+comment4.params=detailScanner
+comment4.target=void\ readItemData(java.util.Scanner)
+comment4.text=\n\ Passed\ a\ scanner,\ assign\ relevant\ values\ to\ field\ variables.\n
+numComments=5

Semester 2/Programming 2/Project/Part 2/Periodical.java

@@ -3,7 +3,7 @@
  * Subclass of LibraryItem to create a periodical ( e.g. newspaper, tabloid ).
  * 
  * @George Wilkinson
- * @1.0
+ * @2.3
  */
 
 import java.util.Scanner;
@@ -12,13 +12,39 @@ public class Periodical extends PrintedItem
 {
     private String publicationDate;
     
+    /**
+     * Constructor for objects of class Periodical
+     * Since all field variables initialise as null, nothing should happen here.
+     */
     public Periodical(){}
     
+    /*
+     * Return value of @publicationDate
+     */
+    public String getPublicationDate()
+    {
+        return publicationDate;
+    }
+    
+    /*
+     * Set value of @publicationDate
+     */
+    public void setPublicationDate( String publicationDate )
+    {
+        this.publicationDate = publicationDate;
+    }
+    
+    /*
+     * Print to terminal, relevant field variable's values.
+     */
     public void printDetails() {
         System.out.println( "Publication Date: " + publicationDate );
         super.printDetails();
     }
     
+    /*
+     * Passed a scanner, assign relevant values to field variables.
+     */
     public void readItemData( Scanner detailScanner ){
         if ( detailScanner != null ) {
             this.publicationDate = detailScanner.next().trim();

Semester 2/Programming 2/Project/Part 2/PrintedItem.java

@@ -1,14 +1,12 @@
 
 /**
- * Write a description of class PrintedItem here.
+ * Subclass of LibraryItem to create objects of printed items in a library.
  * 
- * @author (your name) 
+ * @George Wilkinson
- * @version (a version number or a date)
+ * @1.0
  */
 
 import java.util.Scanner;
-import java.util.ArrayList;
-import java.util.NoSuchElementException;
 
 public abstract class PrintedItem extends LibraryItem
 {