Stack Implementations

1
Stack Implementations

• Chapter 21

2
Chapter Contents

• A Linked Implementation
• An Array-Based Implementation
• A Vector-Based Implementation

3
A Linked Implementation

• When using a chain of linked nodes to implement a
  stack
• The first node should reference the stack's top

Fig. 21-1 A chain of linked nodes that implements
a stack.
4
A Linked Implementation

• Data field and constructor
• Each node an instance of class Node

public class LinkedStack implements
StackInterface, java.io.Serializable private
Node topNode // references first node in
chain public LinkedStack() topNode null
// end default constructor . . .
private class Node implements java.io.Serializable
private Object data // entry in
stack private Node next // link to next
node lt Constructors and the methods getData,
setData, getNextNode, and setNextNode are
here. gt . . . // end Node
5
A Linked Implementation
Fig. 21-2 Before and after final line in push()
(page 479)
6
A Linked Implementation
Fig. 21-3 After a pop() (page 480)
7
An Array-Based Implementation

• When using an array to implement a stack
• The array's first element should represent the
  bottom of the stack
• The last occupied location in the array
  represents the stack's top
• This avoids shifting of elements of the array if
  it were done the other way around

8
An Array-Based Implementation
bad...
good...
Fig. 21-4 An array that implements a stack its
first location references (a) the top of the
stack (b) the bottom of the stack
9
An Array-Based Implementation

• Data fields and constructors

public class ArrayStack implements
StackInterface, java.io.Serializable pr
ivate Object stack private int topIndex
// index of top entry private static final int
DEFAULT_MAX_SIZE 50 public ArrayStack() sta
ck new ObjectDEFAULT_MAX_SIZE topIndex
-1 // end default constructor public
ArrayStack(int maxSize) stack new
ObjectmaxSize topIndex -1 // end
constructor . . .
10
An Array-Based Implementation
Sloppy...
...Better
Fig. 21-5 pop() methods (a) only decrement
topIndex (b) set stacktopIndexnull then
decrement topIndex
11
A Vector-Based Implementation

• When using a vector to implement a stack
• Vector's first element should represent the
  bottom of the stack
• Last occupied location in the vector represents
  the stack's top
• Based on an array that can be expanded
  dynamically
• Performance similar to array-based implementation

12
A Vector-Based Implementation

• Data fields and constructors

import java.util.Vectorpublic class VectorStack
implements StackInterface, java.io.Serializable
public VectorStack() // vector doubles in size
if necessary stack new Vector()
public VectorStack(int maxSize) stack new
Vector(maxSize) . . .