Download Data Structures -

--
Java Software Solutions
Data Structures
Lewis and Loftus
Introduction
All rights reserved.
1
• Let’s explore some advanced techniques for o
and managing information
Copyright 1997 by John Lewis and William Loftus.
dynamic structures
Abstract Data Types (ADTs)
linked lists
queues
stacks
• Chapter 16 focuses on:
–
–
–
–
–
Chapter 16
Java Software Solutions
Lewis and Loftus
Static vs. Dynamic Structures
• A static data structure has a fixed size
• This meaning is different than those associa
static modifier
• Arrays are static; once you define the numb
elements it can hold, it doesn’t change
Copyright 1997 by John Lewis and William Loftus.
All rights reserved.
2
• A dynamic data structure grows and shrinks a
by the information it contains
Chapter 16
Java Software Solutions
Object References
Lewis and Loftus
• Recall that an object is
reference
a variable that sto
the address of an object
All rights reserved.
3
• A reference can also be called a pointer
student
Copyright 1997 by John Lewis and William Loftus.
John Smith
40725
3.57
• They are often depicted graphically:
•
Chapter 16
Java Software Solutions
References as Links
Lewis and Loftus
• Object references can be used
links
to
between
create
objects
John Smith
40725
3.57
All rights reserved.
Jane Jones
58821
3.72
Copyright 1997 by John Lewis and William Loftus.
4
• Suppose Student
a
class contained a reference t
another Student
object
•
Chapter 16
Java Software Solutions
References as Links
Lewis and Loftus
All rights reserved.
5
• References can be used to create a variety o
structures, such as a: linked list
•studentList
•
•
•
•
Copyright 1997 by John Lewis and William Loftus.
• See Library.java
•
Chapter 16
Abstraction
Java Software Solutions
Lewis and Loftus
• Our data structures should be abstractions
is not abstra
• That is, they should hide details as appropr
• This helps manage complexity
• Our original Library solution
Copyright 1997 by John Lewis and William Loftus.
All rights reserved.
6
• One problem is that we use a public variable
links
•
Chapter 16
Java Software Solutions
Abstract Data Types
Lewis and Loftus
• An abstract data(ADT)
type is an organized collec
of information and a set of operations used
that information
• The set of operations define the interface t
• As long as the ADT accurately fulfills the p
the interface, it doesn't really matter how
implemented
Copyright 1997 by John Lewis and William Loftus.
All rights reserved.
7
• Objects are a perfect programming mechanism
ADTs because their internal details are enca
•
Chapter 16
Java Software Solutions
Coupling and Cohesion
Lewis and Loftus
• A well-defined ADT attempts to minimize coup
while maximizing cohesion
• Coupling is the strength of the relationship
components
• Cohesion is the strength of the relationship
parts of one component
Copyright 1997 by John Lewis and William Loftus.
All rights reserved.
8
• We want to formally specify a simple relatio
between the ADT and the outer world, and put
things that relate to the ADT management ins
Chapter 16
Java Software Solutions
Library Revisited
Lewis and Loftus
• A better version of the Library solution wou
book_list object that provides services such
– add a book to the list
– print the book list
–
• The book_listobject in turn interacts with i
Book objects
All rights reserved.
9
• Each Bookobject governs its own references p
Copyright 1997 by John Lewis and William Loftus.
• See Library2.java
Chapter 16
Java Software Solutions
Adding a Node
Lewis and Loftus
• To add a new node to the end of a linked lis
list looking for the last node, then add the
current
Copyright 1997 by John Lewis and William Loftus.
All rights reserved.
10
• The last node is the one withreference
a null next
•
...
Chapter 16
Java Software Solutions
Other List Operations
Lewis and Loftus
• You may also want to perform such operations
– add a node to the front of the list
– add a node somewhere in the middle of the list
– delete a node from the list
–
• Each operation can be defined separately as
method
Copyright 1997 by John Lewis and William Loftus.
All rights reserved.
11
• How an operation is implemented depends on t
underlying representation of the data struct
Chapter 16
Java Software Solutions
Lewis and Loftus
Other Dynamic List Implementations
Copyright 1997 by John Lewis and William Loftus.
All rights reserved.
12
• It may be convenient to implement
doubly
as list as
linked list, with next and previous referenc
list
Chapter 16
Java Software Solutions
Lewis and Loftus
Other Dynamic List Implementations
list
count: 4
front
rear
Copyright 1997 by John Lewis and William Loftus.
All rights reserved.
13
• It may also be convenient to use a separate
with references to both the front and rear o
Chapter 16
Java Software Solutions
Library Revisited
Lewis and Loftus
• Another problem with the existing Library so
that the
Book class contains the reference to t
object in the list
• Ideally, we would like to separate the data
management from the information it holds
• The objects we want to store in the list sho
to be involved with the list references
Copyright 1997 by John Lewis and William Loftus.
All rights reserved.
14
• As we explore other data structures, we will
separation
Chapter 16
Queues
Java Software Solutions
Lewis and Loftus
First-I
• A queue ADT is similar to a list but adds it
the end of the list and removes them from th
Copyright 1997 by John Lewis and William Loftus.
remove
All rights reserved.
15
a line of people at a bank teller’
• It is called a FIFO data structure:
add
• Analogy:
Chapter 16
Queues
Java Software Solutions
Lewis and Loftus
• We can define the operations on a queue as f
– enqueue - add an item to the rear of the queue
– dequeue - remove an item from the front of the que
– empty - returns true if the queue is empty
–
All rights reserved.
16
• By operating on the Object
class, any object can b
stored in the queue
Copyright 1997 by John Lewis and William Loftus.
• See QTrek.java
Chapter 16
Stacks
Java Software Solutions
Lewis and Loftus
• A stack ADT is also linear, like a list or q
• Items are added and removed from only one en
stack
All rights reserved.
17
Last-In, First-Out
Copyright 1997 by John Lewis and William Loftus.
a stack of plates
• It is therefore LIFO:
• Analogy:
Chapter 16
Stacks
Java Software Solutions
add
Lewis and Loftus
remove
Copyright 1997 by John Lewis and William Loftus.
All rights reserved.
• Stacks are often drawn vertically:
Chapter 16
18
Stacks
Java Software Solutions
Lewis and Loftus
push - add an item to the top of the stack
pop - remove an item from the top of the stack
peek - retrieves the top item without removing it
empty - returns true if the stack is empty
• Some stack operations:
–
–
–
–
–
All rights reserved.
19
• The java.utilpackage contains
Stacka class,
which is implemented Vector
using a
Copyright 1997 by John Lewis and William Loftus.
• See Decode.java
Chapter 16