Simple Dynamic Data (Linked Lists)

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Simple Dynamic Data(Linked Lists)
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The Ghost of Things to Come!

• At this point were trying to get you to come to
  grips with the realities of a real language
  before discussing the Object Oriented details.
• That will actually involve turning your mind
  inside out!
• For now we want to essentially get you to convert
  some of the Pseudocode algorithms into
  Simplified Java

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Java Records?

• Java has no record
• Instead Java will use classes to perform this
  function
• For example, a classic student record becomes
• class StudentRecord
• String name
• double gpa
• Now for the big surprise

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No static records

• In Pseudocode we could say
• sr isoftype StudentRecord
• and/or
• srp isoftype Ptr toa StudentRecord
• srp lt- new(StudentRecord)
• In Java there is no equivalent to
• sr isoftype StudentRecord
• In Java we must ALWAYS make objects which are
  dynamic allocations of data in this style
• srp lt- new(StudentRecord)

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In Summary
StudentRec definesa record name isoftype
String gpa isoftype Num endrecord // StudentRec

• Static Allocation
• ts isoftype StudentRec

• Dynamic Allocation
• tsp isoftype Ptr toa StudentRec
• tsp lt- new(StudentRec)

Java has no equivalent

• In Java
• Classes replace records
• References replace Pointers
• Symbols required to tell the difference are not
  needed!

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Java References

• In pseudocode we said
• srp isoftype Ptr toa StudentRecord
• making srp a pointer
• The equivalent in Java looks like this
• StudentRecord srr
• This is called a reference. It is in many ways
  just like a pointer. It points or refers to some
  dynamic memory which contains an Object

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How do we make an Object?

• In a very similar fashion to the way we made
  dynamic allocations
• StudentRecord srr
• srr new StudentRecord()
• Now we can access the fields almost like
  Pseudocode
• srr.name Bob Smith
• srr.gpa 4.0 // Way to go Bob!
• Why no
• Because theres no need!!!

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Compare Contrast

• Pseudocode
• StudentRec definesa record
• name isoftype String
• gpa isoftype Num
• endrecord // StudentRec
• srp isoftype Ptr toa StudentRec
• srp lt- new(StudentRec)
• srp.name lt- Bob
• srp.gpa lt- 4.0

• Java
• Class StudentRec
• String name
• double gpa
• StudentRec srr
• srr new StudentRec()
• srr.name Bob
• srr.gpa 4.0

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Some Details

• Unlike Pseudocode we wont define these classes
  in the code like records.
• Well need to create each class in its own file.
• And the file name must exactly match the class
  name
• class StudentRecord
• String name
• double gpa
• Must be in a file named StudentRecord.java
• And must be compiled (javac StudentRecord.java)
  before use

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By now...

• You must be dying to make a linked list!
• Lets start with the Node (Well have it hold
  ints)
• class LLNode
• int data
• LLNode next
• See the similarity to the pseudocode version?

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Pseudocode version

• procedure addInOrder(cur iot in/out Ptr toa
  LLNode,
• newData iot in Num)
• temp isoftype Ptr toa LLNode
• if(cur NIL OR cur.data gt newdata) then
• temp lt- new(LLNode)
• temp.data lt- newData
• temp.next lt- cur
• cur lt- temp
• else
• addinOrder(cur.next, newData)
• endif
• endprocedure // addInOrder

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Convert to Java Bad Idea

• public void addInOrder(LLNode cur, int newData)
• LLNode temp
• if(cur null cur.data gt newdata)
• temp new LLNode()
• temp.data newData
• temp.next cur
• cur temp
• else
• addinOrder(cur.next, newData)
• // addInOrder

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The Big Problem!

• public void addInOrder(LLNode cur, int newData)
• LLNode temp
• if(cur null cur.data gt newdata)
• temp new LLNode()
• temp.data newData
• temp.next cur
• cur temp
• else
• addinOrder(cur.next, newData)
• // addInOrder

Not an in/out parameter!
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One Solution

• public LLNode addInOrder(LLNode cur, int newData)
  
• LLNode temp
• if(cur null cur.data gt newdata)
• temp new LLNode()
• temp.data newData
• temp.next cur
• cur temp
• return cur
• else
• addinOrder(cur.next, newData)
• // addInOrder

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Necessary Adjustments

• public LLNode addInOrder(LLNode cur, int newData)
  
• LLNode temp
• if(cur null cur.data gt newdata)
• temp new LLNode()
• temp.data newData
• temp.next cur
• cur temp
• return cur
• else
• cur.next addinOrder(cur.next, newData)
• return cur // No change!!!
• // addInOrder

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How do I call this?

• Before
• addInOrder(head, 7)
• Now
• head addInOrder(head, 7)
• Consider

42
84
96
head
3
92
98
head
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Lets try a traversal

• This will be simple since it didnt use in/out
  parameters!
• public void traverse(LLNode cur)
• if(cur ! null)
• System.out.println(cur.data)
• traverse(cur.next)
• // if
• // traverse

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Complete Program

• class LLDemo
• public static LLNode addInOrder(LLNode cur,
• int
  newData)
• LLNode temp
• if(cur null cur.data gt newData)
• temp new LLNode()
• temp.data newData
• temp.next cur
• cur temp
• return cur
• else
• cur.next addInOrder(cur.next, newData)
• return cur // No change!!!
• // addInOrder

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• // class LLDemo (continued)
• public static void traverse(LLNode cur)
• if(cur ! null)
• System.out.println(cur.data)
• traverse(cur.next)
• // if
• // traverse
• public static void menu()
• System.out.println("Enter a to add")
• System.out.println("Enter t to traverse")
• System.out.println("Enter q to quit")
• // menu

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• // class LLDemo (continued)
• public static void main(String args)
• LLNode head null
• char response
• String input
• int newData

Continued
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• // class LLDemo (continued)
• do
• menu()
• input IOGadget.readLine("Enter
  choice")
• response input.charAt(0)
• if(response 'a')
• input IOGadget.readLine("Enter an
  int")
• newData Integer.parseInt(input)
• head addInOrder(head, newData)
• else if(response 't')
• System.out.println("Traversing")
• traverse(head)
• else if(response ! 'q')
• System.out.println("What?")
• while(response ! 'q')
• // main

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