1. Stack Implementations Chapter 6 Copyright ©2012 by Pearson Education, Inc. All rights reserved

2. Contents A Linked Implementation An Array-Based Implementation A Vector-Based Implementation  Java Class Library: The Class Vector  Using a Vector to Implement the ADT Stack Copyright ©2012 by Pearson Education, Inc. All rights reserved

3. Objectives Implement ADT stack by using either  Linked chain  Array  Vector Compare and contrast various implementations and their performance Copyright ©2012 by Pearson Education, Inc. All rights reserved

4. Linked Implementation Consider push, pop, peek  Each involves top of stack Best to put top of stack at head node  Fastest, easiest to access Java will manage reclaiming memory without instruction from programmer Note source code for linked implementation  Listing 6-1 Listing 6-1 Note: Code listing files must be in same folder as PowerPoint files for links to work Note: Code listing files must be in same folder as PowerPoint files for links to work Copyright ©2012 by Pearson Education, Inc. All rights reserved

5. Figure 6-1 A chain of linked nodes that implements a stack Copyright ©2012 by Pearson Education, Inc. All rights reserved

6. FIGURE 6-2 (a) A new node that references the node at the top of the stack; (b) the new node is now at the top of the stack Copyright ©2012 by Pearson Education, Inc. All rights reserved

7. Linked Implementation Copyright ©2012 by Pearson Education, Inc. All rights reserved

8. Figure 6-3 The stack (a) before the first node in the chain is deleted Copyright ©2012 by Pearson Education, Inc. All rights reserved

9. Figure 6-3 The stack (b) after the first node in the chain is deleted Copyright ©2012 by Pearson Education, Inc. All rights reserved

10. Array Based Implementation Again the question:  Were to place the top entry? More efficient operations with bottom of stack at beginning of array  Top of stack at last occupied entry Must consider memory wastage of unused array elements Copyright ©2012 by Pearson Education, Inc. All rights reserved

11. Figure 6-4 An array that implements a stack; its first location references (a) the top entry in the stack; Copyright ©2012 by Pearson Education, Inc. All rights reserved

12. Figure 6-4 An array that implements a stack; its first location references (b) the bottom entry in the stack; Copyright ©2012 by Pearson Education, Inc. All rights reserved

13. Adding to the Top Copyright ©2012 by Pearson Education, Inc. All rights reserved

14. Retrieving the Top Copyright ©2012 by Pearson Education, Inc. All rights reserved

15. Figure 6-5 An array-based stack after its top entry is removed by (a) decrementing topIndex ; Copyright ©2012 by Pearson Education, Inc. All rights reserved

16. Figure 6-5 An array-based stack after its top entry is removed by (b) setting stack[topIndex] to null and then decrementing topIndex Copyright ©2012 by Pearson Education, Inc. All rights reserved

17. Method Pop Copyright ©2012 by Pearson Education, Inc. All rights reserved

18. Vector-Based Implementation Vector is a structure which behaves like a high level array  Has methods to access entries  Grows in size as needed (hidden from client) Copyright ©2012 by Pearson Education, Inc. All rights reserved

19. Figure 6-6 A client using the methods given in StackInterface ; these methods interact with a vector’s methods to perform stack operations Copyright ©2012 by Pearson Education, Inc. All rights reserved

20. Constructors and Methods of Vector public Vector() public Vector(int initialCapacity) public boolean add(T newEntry) public T remove(int index) public void clear() public T lastElement() public boolean isEmpty() public int size() Copyright ©2012 by Pearson Education, Inc. All rights reserved

21. Using a Vector to Implement ADT Stack Similar to using an array  But easier First element is bottom of stack Vector adjusts size automatically  Our stack implementation need not deal with adjusting size View outline, Listing 6-3Listing 6-3 Copyright ©2012 by Pearson Education, Inc. All rights reserved

22. Stack Methods for Vector Implementation Copyright ©2012 by Pearson Education, Inc. All rights reserved

23. Should VectorStack Extend Vector? If we use inheritance  It would have available all methods of Vector  Would allow access to any element  This violates premise of ADT Stack Design decision  Do NOT use inheritance Copyright ©2012 by Pearson Education, Inc. All rights reserved

24. End Chapter 6 Copyright ©2012 by Pearson Education, Inc. All rights reserved