Chapter 10 1

Dynamic Data Structures and Generics

Chapter 10

Chapter 10 2

Reminders

• Project 6 due Nov 03 @ 10:30 pm

• Project 5 grades released (or by tonight): regrade requests due by next Friday

• Exam 2: handed back next week, solution discussed next week

Chapter 10 3

Introduction

• A data structure is a construct used to organize data in a specific way.

• An array is a static data structure.• Dynamic data structures can grow and shrink

while a program is running.• Vectors and linked data structures are

dynamic.

Chapter 10 4

Introduction to Vectors, cont.

• Vectors serve the same purposes as arrays, but can change in length while a program is running.

• This added flexibility comes at a price:– Vectors are less efficient than arrays.– The base type of a vector must be a class

type rather than a primitive type. (Automatic boxing and unboxing make this requirement less significant than it used to be.)

Chapter 10 5

Using Vectors• The definition of class Vector must be

imported.import java.util.*;

• to create and name a vectorVector<String> v = new Vector<String>(20);

– The vector v stores objects of class String and has an initial capacity of 20.

• Don’t need to specify the class typeVector v = new Vector(20);

- Can store any kind of object

Chapter 10 6

Using Vectors, cont.

– When more capacity is needed, the system allocates more memory automatically.

– If the initial capacity was sufficient, the code is more efficient.

• In this example, the base type is type String.– Any class can be used as the base type.– But, wrapper classes MUST be used for

primitive types.

Chapter 10 7

Adding, Getting, and Setting Values

• to add an elementv.addElement(“Hello!”);

• to get the value of an elementString temp = v.elementAt(index);

• to change the value of an existing elementv.setElementAt(“Hi, Mom!”, index);

*** element must already exist to use setElementAt ***

Chapter 10 8

addElement vs. insertElementAt• Remember that add element always adds an element at the end of the

Vector. If the Vector v currently contains:

• After v.addElement(“E”):

• If we had done v.insertElementAt(“E”,2) instead of the addElement line above:

• Finally, if we had done v.insertElementAt(“E”,4) instead of the two lines above, it would be the same as calling v.addElement(“E”):

“A” “B” “C” “D” size = 4

“A” “B” “C” “D” size = 5“E”

“A” “B” “E” “C” size = 5“D”

“A” “B” “C” “D” size = 5“E”

Chapter 10 9

setElementAt vs. insertElementAt• setElementAt changes an existing element while insertElementAt inserts a new element. The index parameter of setElementAt must be less than the size of the vector.

• Example: Our original Vector v:

• After v.setElementAt(“E”,2):

• After v.insertElementAt(“E”,2): (Instead of line above)

“A” “B” “C” “D” size = 4

“A” “B” “E” “D” size = 4

“A” “B” “E” “C” size = 5“D”

Chapter 10 10

Size and Indices

• to learn the maximum capacity of the vectorint maxSize = v.capacity();

• To learn the size of the vectorint howMany = v.size();

• The indices range from 0 to v.size()-1.

Chapter 10 11

Chapter 10 12

Introduction to Linked Data Structures

• A linked data structure is a collection of objects (called nodes), each containing data and a (potential) reference to (at least) one other node.

Chapter 10 13

Linked Lists

• The predefined LinkedList class is part of the java.util package.

• Nevertheless, to learn how linked data structures work, we’ll construct a simplified example of a linked list.

Chapter 10 14

Linked Lists, cont.

Chapter 10 15

Linked Lists, cont.

• Each node is an object of a class that has (at least) two instance variables:– the data– the link.

Chapter 10 16

Chapter 10 17

Moving Down a Linked List

Chapter 10 18

Adding a Node at the Start

Chapter 10 19

Inner Classes

• An inner class is a class defined within another class.

Chapter 10 20

Defining an Inner Class

public class OuterClass

{

OuterClass_Instance_Variables

OuterClass_Methods

private class InnerClass

{

InnerClass_Instance_Variables

InnerClass_Methods

}

}

Chapter 10 21

Access to Members

• The inner and outer classes’ methods have access to each other’s methods and instance variables, even when they are declared private.

Chapter 10 22

Node Inner Classes

• By making the node class an inner class, data structure classes become self-contained.

• Further, the accessor and mutator methods of the inner class can be eliminated since instance variables of an inner class are accessible directly.

Chapter 10 23

Chapter 10 24

Chapter 10 25

Iterators

• With a collection of objects, such as the nodes of a linked list, we often need to “step through” all the objects to perform some action on each object.

• An iterator allows us to “step through” a collection of objects.

Chapter 10 26

Iterators, cont.

• The loop control variable of a for loop functions as an iterator for an array.for (int i = 0; i < a.length, i++)

process a[i];

Chapter 10 27

Iterators, cont.

• Similarly, an instance variable capable of referencing a node, can serve the same purpose as the loop control variable in a for loop.

• Another instance variable capable of referencing a node can “follow behind” to provide access to the previous node.

Chapter 10 28

Advancing to the Next Node

Chapter 10 29

Adding a Node

Chapter 10 30

Deleting a Node

Chapter 10 31

Variations on a Linked List

• A reference to the last node in a linked list can be useful.…

public ListNode head;

public ListNode tail;

…

• A linked list can contain (or reference) any kind of data.

Chapter 10 32

Variations on a Linked List, cont.

• A linked list can contain different kinds of objectsprivate class ListNode

{

private Object data;

private ListNode link;

...

}

Chapter 10 33

Variations on a Linked List, cont.

• An additional reference can be added to reference the previous node, producing a doubly-linked list.private class ListNode

{

private Object data;

private ListNode next;

private ListNode previous;

...

}

Chapter 10 34

Variations on a Linked List, cont.

Chapter 10 35

Variations on a Linked List, cont.

• The last node in a singly-linked list can reference the first node, producing a circularly-linked list.

• The last node in a doubly-linked list can reference the first node with its next reference, and the first node can reference the last node with its previous reference, producing a doubly-circularly-linked list.

Chapter 10 36

Introduction to Generics

• Java 5.0 allows definitions, called generics, that include parameters for types.

• Generics can be subtle and full of pitfalls.• We provide an introduction to generics.• Serious programming with generics is

presented in more advanced texts.

Chapter 10 37

Generic Basics

• Classes and methods can have a type parameter.

• Any class type can be substituted for the type parameter, producing a specific class type or method.

Chapter 10 38

• class Sample<T>

Generic Basics, cont.

Chapter 10 39

Generic Basics, cont.

• A class definition with a type parameter is stored in a file and compiled just like any other class.

• When used in code a class type must be specified so that it can be substituted for the type parameter.

Chapter 10 40

Generic Basics, cont.

• exampleSample<String> o1 = new Sample<String>();

o1.setData(“Hello”);

Sample<Species> o2 = new Sample<Species>();

Species s = new Species();

<code to set the data for object s>

o2.setData(s);

Chapter 10 41

Generic Basics, cont.

• You cannot substitute a primitive type for a type parameter.

• You must instead use a class type.

Chapter 10 42

Chapter 10 43

Chapter 10 44

Chapter 10 45

Generic Constructor

• The class name in a parameterized class definition has a type parameter attached.

• But, a generic constructor name has no type parameter and the type parameter is not used in the heading of the constructor definition.public LinkedList()

notpublic LinkedList<e>() // ILLEGAL

Chapter 10 46

Summary

• You have become familiar with vectors.• You have learned about linked data

structures in Java.• You have learned how to manipulate linked

lists.• You have learned to use inner classes in

defining linked data structures

Chapter 10 47

Summary, cont.

• You have learned about iterators.• You have learned about generics (parameters

for types).