1. Simple Dynamic Data (Linked Lists)

2. The Ghost of Things to Come!
At this point we’re 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”

3. 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

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

5. In Summary Java has no equivalent StudentRec definesa record
name isoftype String
gpa isoftype Num
endrecord // StudentRec
Static Allocation
ts isoftype StudentRec
Dynamic Allocation
tsp isoftype Ptr toa StudentRec
tsp <- new(StudentRec)
Java has no
equivalent
In Java
Classes replace records
References replace Pointers
Symbols required to tell the difference are not needed! ^

6. 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

7. 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 there’s no need!!!

8. Compare & Contrast Pseudocode StudentRec definesa record
name isoftype String
gpa isoftype Num
endrecord // StudentRec
srp isoftype Ptr toa StudentRec
srp <- new(StudentRec)
srp^.name <- “Bob”
srp^.gpa <- 4.0
Java
Class StudentRec {
String name;
double gpa; }
StudentRec srr;
srr = new StudentRec();
srr.name = “Bob”;
srr.gpa = 4.0;

9. Some Details
Unlike Pseudocode we won’t define these classes in the code like records.
We’ll 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

10. By now... You must be dying to make a linked list!
Let’s start with the Node (We’ll have it hold ints)
class LLNode {
int data;
LLNode next; }
See the similarity to the pseudocode version?

11. 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 > newdata) then
temp <- new(LLNode)
temp^.data <- newData
temp^.next <- cur
cur <- temp
else
addinOrder(cur^.next, newData)
endif
endprocedure // addInOrder

12. Convert to Java: Bad Idea
public void addInOrder(LLNode cur, int newData) {
LLNode temp;
if(cur == null || cur.data > newdata) {
temp = new LLNode();
temp.data = newData;
temp.next = cur;
cur = temp; }
else {
addinOrder(cur.next, newData);
} // addInOrder

13. The Big Problem! Not an in/out parameter!
public void addInOrder(LLNode cur, int newData) {
LLNode temp;
if(cur == null || cur.data > newdata) {
temp = new LLNode();
temp.data = newData;
temp.next = cur;
cur = temp; }
else {
addinOrder(cur.next, newData);
} // addInOrder
Not an in/out parameter!

14. One Solution public LLNode addInOrder(LLNode cur, int newData) {
LLNode temp;
if(cur == null || cur.data > newdata) {
temp = new LLNode();
temp.data = newData;
temp.next = cur;
cur = temp;
return cur; }
else {
addinOrder(cur.next, newData);
} // addInOrder

15. Necessary Adjustments
public LLNode addInOrder(LLNode cur, int newData) {
LLNode temp;
if(cur == null || cur.data > 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

16. How do I call this? Before addInOrder(head, 7); Now
head = addInOrder(head, 7);
Consider 42 84 96
head 3 92 98
head

17. Let’s try a traversal
This will be simple since it didn’t use in/out parameters!
public void traverse(LLNode cur) {
if(cur != null) {
System.out.println(cur.data);
traverse(cur.next);
} // if
} // traverse

18. Complete Program class LLDemo {
public static LLNode addInOrder(LLNode cur,
int newData) {
LLNode temp;
if(cur == null || cur.data > 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

19. // 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

20. Continued // class LLDemo (continued)
public static void main(String args[]) {
LLNode head = null;
char response;
String input;
int newData;
Continued

21. // 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
} // LLDemo