1. Data Structures Using Java1 Chapter 6 Stacks

2. Data Structures Using Java2 Chapter Objectives Learn about stacks Examine various stack operations Learn how to implement a stack as an array Learn how to implement a stack as a linked list Discover stack applications Learn to use a stack to remove recursion

3. Data Structures Using Java3 Stacks Definition: –list of homogeneous elements –addition and deletion of elements occurs only at one end, called the top of the stack Last In First Out (LIFO) data structure Used to implement method calls Used to convert recursive algorithms (especially not tail recursive) into nonrecursive algorithms

4. Data Structures Using Java4 Various Types of Stacks

5. Data Structures Using Java5 LIFO Last In First Out (LIFO) data structure –Top element of stack is last element to be added to stack –Elements added and removed from one end (top) –Item added last are removed first

6. Data Structures Using Java6 Empty Stack

7. Data Structures Using Java7 Stack Operations

8. Data Structures Using Java8 Basic Operations on a Stack initializeStack: Initializes the stack to an empty state isEmptyStack: Checks whether the stack is empty. If empty, it returns true; otherwise, it returns false isFullStack: Checks whether the stack is full. If full, it returns true; otherwise, it returns false

9. Data Structures Using Java9 Basic Operations on a Stack push: –Add new element to the top of the stack –The input consists of the stack and the new element –Prior to this operation, the stack must exist and must not be full

10. Data Structures Using Java10 Basic Operations on a Stack top: Returns the top element of the stack. Prior to this operation, the stack must exist and must not be empty pop: Removes the top element of the stack. Prior to this operation, the stack must exist and must not be empty

11. Data Structures Using Java11 Example of a Stack

12. Data Structures Using Java12 Empty Stack

13. Data Structures Using Java13 initializeStack public void initializeStack() { for(int i = 0; i < stackTop; i++) list[i] = null; stackTop = 0; }//end initializeStack

14. Data Structures Using Java14 emptyStack and fullStack public boolean isEmptyStack() { return(stackTop == 0); }//end isEmptyStack public boolean isFullStack() { return(stackTop == maxStackSize); }//end isFullStack

15. Data Structures Using Java15 Push

16. Data Structures Using Java16 Push public void push(DataElement newItem) throws StackOverflowException { if(isFullStack()) throw new StackOverflowException(); list[stackTop] = newItem.getCopy(); //add newItem at the //top of the stack stackTop++; //increment stackTop }//end push

17. Data Structures Using Java17 Return Top Element public DataElement top() throws StackUnderflowException { if(isEmptyStack()) throw new StackUnderflowException(); DataElement temp = list[stackTop - 1].getCopy(); return temp; }//end top

18. Data Structures Using Java18 Pop public void pop() throws StackUnderflowException { if(isEmptyStack()) throw new StackUnderflowException(); stackTop--; //decrement stackTop list[stackTop] = null; }//end pop

19. Data Structures Using Java19 Pop

20. Data Structures Using Java20 copy private void copy(StackClass otherStack) { list = null; System.gc(); maxStackSize = otherStack.maxStackSize; stackTop = otherStack.stackTop; list = new DataElement[maxStackSize]; //copy otherStack into this stack for(int i = 0; i < stackTop; i++) list[i] = otherStack.list[i].getCopy(); }//end copy 6

21. Data Structures Using Java21 Constructors //constructor with a parameter public StackClass(int stackSize) { if(stackSize <= 0) { System.err.println(“The size of the array to implement “ + “the stack must be positive.”); System.err.println(“Creating an array of size 100.”); maxStackSize = 100; } else maxStackSize = stackSize; //set the stack size to //the value specified by //the parameter stackSize stackTop = 0; //set stackTop to 0 list = new DataElement[maxStackSize]; //create the array }//end constructor

22. Data Structures Using Java22 Constructors //default constructor public StackClass() { maxStackSize = 100; stackTop = 0; //set stackTop to 0 list = new DataElement[maxStackSize]; //create array }//end default constructor

23. Data Structures Using Java23 Copy Constructor and copyStack public StackClass(StackClass otherStack) { copy(otherStack); }//end copy constructor public void copyStack(StackClass otherStack) { if(this != otherStack) //avoid self-copy copy(otherStack); }//end copyStack

24. Data Structures Using Java24 Time Complexity of Operations of class stackType

25. Data Structures Using Java25 Programming Example: Highest GPA InputThe program reads an input file consisting of each student’s GPA, followed by the student’s name. Sample data is: 3.8 Lisa 3.6 John 3.9 Susan 3.7 Kathy 3.4 Jason 3.9 David 3.4 Jack

26. Data Structures Using Java26 Programming Example: Highest GPA (Algorithm) 1.Declare the variables 2.Create a DecimalFormat object to output a decimal number to two decimal places 3.Open the input file 4.If the input file does not exist, exit the program 5.Read the next input line

27. Data Structures Using Java27 Highest GPA (Algorithm) 6.while (not end of file) { 6.a. Tokenize the input line 6.b. Get the next GPA 6.c. Get the next name 6.d. if (GPA > highestGPA) { 6.d.i initialize stack 6.d.ii push(stack, student name) 6.d.iii highestGPA = GPA } 6.e. else if(GPA is equal to highestGPA) push(stack, student name) 6.f Read the next input line }

28. Data Structures Using Java28 Programming Example: Highest GPA (Algorithm) 7.Output the highest GPA. 8.Output the names of the students having the highest GPA.

29. Data Structures Using Java29 Programming Example: Highest GPA (Sample Run) Input File (Ch6_HighestGPAData.txt) 3.4 Holt 3.2 Bolt 2.5 Colt 3.4 Tom 3.8 Ron 3.8 Mickey 3.6 Pluto 3.5 Donald 3.8 Cindy 3.7 Dome 3.9 Andy 3.8 Fox 3.9 Minnie 2.7 Goofy 3.9 Doc 3.4 Danny

30. Data Structures Using Java30 Programming Example: Highest GPA (Sample Run) Output Highest GPA = 3.90 The students holding the highest GPA are: Doc Minnie Andy

31. Data Structures Using Java31 Empty and Nonempty Linked Stack Empty linked stackNonempty linked stack

32. Data Structures Using Java32 Default Constructor public LinkedStackClass() { stackTop = null; }

33. Data Structures Using Java33 initializeStack, isStackEmpty, and isStackFull public void initializeStack() { stackTop = null; }//end initializeStack public boolean isEmptyStack() { return(stackTop == null); } public boolean isFullStack() { return false; }

34. Data Structures Using Java34 Push Stack before the push operation Stack and newNode

35. Data Structures Using Java35 Push Stack after the statement newNode.link = stackTop; executes Stack after the statement stackTop = newNode; executes

36. Data Structures Using Java36 Return Top Element public DataElement top() throws StackUnderflowException { if(stackTop == null) throw new StackUnderflowException(); return stackTop.info.getCopy(); }//end top

37. Data Structures Using Java37 Pop Stack before the pop operation Stack after the statement stackTop = stackTop.link; executes Stack after popping the top element

38. Data Structures Using Java38 Application of Stacks: Postfix Expression Calculator Prefix/Polish Notation Suffix/Postfix/Reverse Polish Notation

39. Data Structures Using Java39 Application of Stacks: Postfix Expression Calculator

40. Data Structures Using Java40 Application of Stacks: Postfix Expression Calculator Stack after pushing 6 Stack after pushing 3 Stack after retrieving the top two elements and popping twice Stack after pushing the result of op1 + op2, which is 9

41. Data Structures Using Java41 Application of Stacks: Postfix Expression Calculator Stack after pushing 2 Stack after retrieving the top two elements and popping twice Stack after pushing the result of op1 * op2, which is 18 Stack after popping the element

42. Data Structures Using Java42 Postfix Expression Calculator (Main Algorithm) Get the next expression while more data to process { a. initialize the stack b. process the expression c. output the result d. get the next expression }

43. Data Structures Using Java43 Nonrecursive Algorithm to Print Linked List current = first; //Line 1 while(current != NULL) //Line 2 { stack.push(current); //Line 3 current = current.link; //Line 4 }

44. Data Structures Using Java44 List After Execution of Statement current = first;

45. Data Structures Using Java45 Repeated Execution of: stack.push(current); current = current.link;

46. Data Structures Using Java46 Java class Stack Java provides a class to implement a stack in a program The name of the Java class defining a stack is Stack The class Stack is contained in the package java.util Table 6-3 lists the members of the class Stack

47. Data Structures Using Java47 Java class Stack

48. Data Structures Using Java48 Chapter Summary Stack Data Structure Last In First Out (LIFO) Stacks Implemented as Arrays Stacks Implemented as Linked Lists Postfix Expression Calculator Nonrecursive Algorithm to Print Linked List Java class Stack