GENERICS AND
ARRAY-BASED LISTS
TOPICS
· (Java) Interface: Comparable
· Primitive
Data Types and Wrapper Classes
· Generics
· ADT: Unordered List
(Array-Based Implementation)
· ADT: Ordered List
(Array-Based Implementation)
OUTLINE
· Reminder: inheritance, interfaces,
class Object.
· The method clone of the class Object is a protected method
inherited by every class in Java. The method clone cannot be invoked by an
object outside the definition of its class.
· It provides a bit-by-bit copy of the object’s data in storage
(shallow copy of object's data) --> In order to make a deep copy of an
object’s data, its class must override the clone method from class Object.
· NOTE: The interface Cloneable has no method headings
that need to be implemented --> Classes that implement this interface
must only redefine the clone() method.
· Example:
public
class Time implements Cloneable {...}
· When writing the clone method, follow these steps:
· NOTE: The method clone of the class Object throws CloneNotSupportedException
· Example: Same method clone() in class Time, Date, Person
public
Object clone() {
try {
return super.clone();
}
catch (CloneNotSupportedException
e) {
return null;
}
}
· NOTE: The method clone returns a reference of the
type Object or the value null --> must typecast the returned
object to a reference of the same type as the class you work with.
· Example:
Time t1 = new Time(11,
12, 13);
Time t2 = (Time) t1.clone();
· If the class uses composition (has instance variables of type
class), then the clone method has to change the values of those instance
variables.
· Example: method clone() in class PersonalInfo
public
Object clone() {
try {
PersonalInfo copy = (PersonalInfo)
super.clone();
copy.birthDate = (Date) birthDate.clone();
copy.fullName = (Person) fullName.clone();
return copy;
}
catch (CloneNotSupportedException
e) {
return null;
}
}
· The interface Comparable has only one method heading,
which is compareTo(not a member of Object)
--> Used to
force a class to provide an appropriate definition of the method compareTo.
It provides a
means of fully ordering objects.
· Values of two objects of the same class can be properly compared (equals
compares only
for equality) Many types have the notion of a natural ordering that describes
whether one value of that type is "less than" or "greater
than" another: numeric values, strings (lexical/alphabetical order),
times, dates, etc. Not all types have a natural ordering (ex: Point)
· NOTE: The interface Comparable has no method headings
that need to be implemented --> Classes that implement this interface
must only redefine the compareTo() method.
· The method compareTo
compares this
object with the object passed for order. Returns a negative integer, zero, or a
positive integer as this object is less than, equal to, or greater than the
object passed.
· Example:
public class Time implements Comparable {...}
· NOTE: If a class implements
multiple interfaces, separate all interfaces names using commas.
· Example:
public
class Time implements Cloneable, Comparable {...}
· Example: method compareTo() in class Time:
public
int compareTo(Object othertime) {
Time temp = (Time) othertime;
int hrDiff = hrs - temp.hrs;
if (hrDiff !=
0)
return hrDiff;
int minDiff = mins - temp.mins;
if (minDiff !=
0)
return minDiff;
return secs - temp.secs;
}
· Example: method compareTo() in class Date:
public int compareTo(Object otherDate) {
Date temp = (Date) otherDate;
int yearDiff = year - temp.year;
if (yearDiff !=
0)
return yearDiff;
int monthDiff = month - temp.month;
if (monthDiff
!= 0)
return monthDiff;
return day - temp.day;
}
· Example: method compareTo() in class Person:
public
int compareTo(Object otherPerson) {
Person temp = (Person) otherPerson;
int compare = lastName.compareTo(temp.lastName);
if(compare == 0)
compare = firstName.compareTo(temp.firstName);
return compare;
}
· Example: method compareTo() in class PersonalInfo:
public
int compareTo(Object other)
{
PersonalInfo
temp = (PersonalInfo) other;
int compare = personID - temp.personID;
if(compare == 0)
compare = fullName.compareTo(temp.fullName);
if(compare == 0)
compare = birthDate.compareTo(temp.birthDate);
return compare;
}
· Check here the (complete) new definition for class Time. (including
clone()
and compareTo())
· Check here the (complete) new definition for class Date. (including
clone()
and compareTo())
· Check here the (complete) new definition for class Person. (including
clone()
and compareTo())
· Check here the (complete) new definition for class PersonalInfo. (including clone() and compareTo())
3. Primitive
Data Types and Wrapper Classes
· Definition: Wrapper
Classes = Classes Integer, Double,
Character, Long, Float, Boolean, etc, provided so that values of
primitive data types can be treated as objects.
· A wrapper is an object whose sole purpose is to hold a
primitive value.
|
Primitive
type |
Wrapper
class |
|
int |
Integer |
|
double |
Double |
|
float |
Float |
|
char |
Character |
|
boolean |
Boolean |
|
long |
Long |
· The Integer class wraps a value of the
primitive type int in an object. An object of
type Integer
contains a single instance variable whose type is int. The class provides several
methods for converting an int to a String and a String to an int, as well as other methods
useful when dealing with an int. Take a look at some methods
in class Integer
· Definition: The conversion between
the primitive type and the wrapper class = boxing and unboxing.
· As of Java Standard Edition 5.0, Java automatically
converts values back and forth between the primitive type and the corresponding
wrapper class = auto-boxing and auto-unboxing.
· How auto-boxing works: if an int is passed in a place where
an Integer
is required, the compiler will make a (behind the scenes) call to the wrapper
class constructor (Integer).
· How auto-unboxing works: if an Integer is passed in a place where
an int is required, the compiler
will make a (behind the scenes) call to the intValue method.
· Similar behavior takes place for the 7 other primitive
types/wrapper classes pairs.
· Example:
|
Auto-boxing
(of the int type) |
Auto-unboxing
(of the Integer type) |
|
int x;
num = 10; //auto boxing Equivalent
to the statement: |
int x;
x = num; //auto-unboxing Equivalent
to the statement: |
· When to use auto-boxing and
auto-unboxing?
Only when there is a mismatch between reference types and primitives (for
example, when you have to put numerical values into a collection - to be
discussed later). It is not appropriate to use them for scientific computing,
or other performance-sensitive numerical code. An Integer is not a perfect substitute
for an int; auto-boxing and unboxing
blur the distinction between primitive types and reference types, but they do
not eliminate it (for example, the wrapper classes have limitations - cannot
change the value stored in an object). Although boxing and unboxing can be
quite convenient, this feature can generate confusion and should be used with
care.
· One important goal of OOP is to provide the ability to write
reusable, generalized code. One important mechanism that supports this goal =
generics. The idea: if the implementation is identical except for the
basic type of the object --> use a generic implementation to describe the
basic functionality. Example: When
sorting an array, the logic in bubble sort is independent of the types of
objects being sorted. Same for searching, inserting, deleting, etc.
· Java supports
generic methods and generic classes. Writing generic classes requires more work
- the constructs of the language are quite complex (and sometimes tricky!)
· Definition: Generics
= powerful means of writing generalized code that can be used by any
class in any hierarchy represented by the type parameter. Class
definitions that include a type parameter are called generic types.
· Definition: Type
parameter =
identifier that specifies a generic type name. Any non-keyword identifier can
be used for the type parameter, but by convention, the parameter starts with an
uppercase letter. The type parameter can be used like other types used in the
definition of a class, but cannot represent primitive types (see the note
below). Also known as type variables - used to:
· Declare the return type of the method
· Declare formal parameters
· Declare local variables
· NOTE: A type parameter
cannot be used everywhere a type name can be used. In particular, the type
parameter cannot be used in simple expressions using new to create a new object. Example:
T someObject = new T();
T[] someArray = new T[SIZE]; --> Compiling ERROR!
· NOTE: A primitive type
cannot be plugged in for a type parameter --> the type plugged in for a type
parameter must always be a reference type. However, Java has automatic boxing
so, for wrapper classes this is not a big restriction (use wrapper classes
instead of primitive data types!). Also, reference types can include arrays.
· Definition: Generic
method =
Method defined using type parameter. The type list precedes the return type.
The type is used as the return type, OR the type is used in more than one
parameter, OR the type is used to declare a local variable. The general syntax
for a generic method is: modifier(s)
<T> methodType methodName(formal
parameters) {...}
· Examples:
//generic method to
print array
public static <T> void print(T[] list) {
for(int i = 0; i < list.length;
i++)
System.out.print(list[i] + "
");
System.out.println();
}
Calls:
Integer[] intList
= {1, 2, 3, 4, 5};
Double[] doubleList = {1.1, 2.2, 3.3};
String[] strList = {"List", "Stack",
"Queue", "Tree"};
print(intList);
print(doubleList);
print(strList);
//generic
method for linear search
public static
<T> int seqSearch(T[] list, T searchItem) {
for(int i = 0; i < list.length; i++)
if(list[i].equals(searchItem))
return i;
return -1;
}
· Generic methods and bounded type
parameters --> There are situations when the type parameter <T> must be restricted. For
example: we plan to design a method to find the larger value of two objects.
The method should work with built-in as well as user-defined classes. Objects
are compared using the method compareTo --> the method should
work only with classes that provide a definition of the method compareTo.
· Examples:
//findMax/2 objects
public static <T extends Comparable<T> > T findMax(T
x, T y) {
return x.compareTo(y)
>= 0? x: y;
}
//findMax/array
public static <T extends Comparable<T> > T findMax(T[] list) {
int maxIndex
= 0;
for(int i
= 0; i < list.length; i++){
Comparable<T> listElem =
(Comparable<T>) list[i];
if(listElem.compareTo(list[maxIndex])
> 0)
maxIndex = i;
}
return list[maxIndex];
}
//bubble sort
public static <T
extends Comparable<T>> void bubbleSort(T[]
list) {
for
(int pass = 0; pass < length - 1; pass++) {
for (int i = 0; i < length - 1; i++) {
Comparable<T> listElem = (Comparable<T>)
list[i];
if (listElem.compareTo(list[i
+ 1]) > 0) {
T temp = list[i];
list[i] = list[i + 1];
list[i + 1] = temp;
}
}
}
}
· NOTE: Always use the keyword
extends
regardless of whether the type parameter extends a class or an interface
· NOTE: If a type parameter is
bounded by more than one class (or interface) class names are separated using
the symbol &
· Definition: Generic class
(parameterized or parametric class) = a class that is defined with a parameter for a type. The
type parameter is included in angular brackets < > after the class name
in the class definition heading. The general syntax for a generic class
is: modifier(s) className
<T> modifier(s) {...}
· Generic classes are used to write a single definition for a set of
related classes.
· NOTE: A class definition
with a type parameter is stored in a file and compiled just like any other
class. Once a parameterized class is compiled, it can be used like any other
class. However, the class type plugged in for the type parameter must be
specified before it can be used in a program.
· NOTE: An instantiation of a
generic class cannot be an array base type --> use an ArrayList instead.
· NOTE: A generic class definition
can have any number of type parameters --> multiple type parameters are
listed in angular brackets just as in the single type parameter case, but are
separated by commas.
· Definition: Abstract Data Type (ADT) = A data
type that specifies the logical properties without the implementation details
(information hiding --> the ADT hides the implementation details from the
programs using the ADT --> the users can use the operations of an ADT
without knowing how they have been implemented).
· ADT = a collection of data and a set of operations on that data
(while a data structure is a construct within a programming language that
stores a collection of data). Describes what the collection does, not how it
does it.
· Data abstraction is the result of ADT operations between
data structures and the program that accesses the data within these data
structures. The goal of data abstraction is to separate the operations on data
from the implementation of these operations. A program should not depend on the
details of an ADT implementation because ADT's properties (domain and operations)
are specified independently of any particular implementation.
· An ADT separates the logical properties of a data type (what
are the possible values, what operations will be needed) from its
implementation. In other words, data abstraction separates the qualities of an
object from the details of how it works.
· ADT properties:
· Set of values (domain)
· Allowable operations on those values.
· Definitions:
· List = Linear data structure
whose components could be accessed sequentially, one after the other. A list is
a collection of elements of the same type.
· Components of a list = List elements OR list
items.
· Head (front) = First element of the list.
· Tail (back, end) = Last element of the list.
· Length of a list = The number of elements in
the list. Conceptually, there is no upper bound for length, but a computer's
memory size is bounded --> "list is full" means the list has
reached maximum length.
· List properties:
· The length of the list could change over time, as new items are
inserted and old items are deleted (varying length).
· All list elements have the same type (homogeneous components).
· Access to list elements is sequential (through an implicit list
cursor --> a pointer that keeps track of the location, while going in a
sequence through the list).
· Linear relationship --> Each element except the head
has a unique predecessor, and each element except the tail has a unique
successor.
· Unordered/unsorted list = A list in which data items
are placed in no particular order; the only relationship between data elements
is the list predecessor and successor relationships.
· Key = The attribute
used to determine the logical/physical order of the list elements.
· Ordered/sorted list = A list in which the list
elements are in an order that is sorted in some way -- either numerically or
alphabetically by the elements themselves, or by a component (key). A sorted
list is a list that is sorted by the value in the key; there is a semantic relationship
among the keys of the items in the list. If a list cannot contain elements with
duplicate keys, it is said to have unique keys.
· Common operations performed on a
list
· Advantage of using ADT Lists over
arrays: Much
easier to perform insertions and deletions (less operations).
· Disadvantage of using ADT Lists over
arrays:
Direct access of a component is impossible (advance first to the element with
index i, then print; with arrays could just print the
element with index i).
· We prefere using a list ADT when the
frequency of inserting and deleting elements is significantly greater than the frequency
of selecting, storing or retrieving existing elements.
· To implement the List ADT, we must
1) Choose a concrete data representation for the list.
An effective, convenient, and common way to process a list is to store it in an
array. Initially the size of the array is larger than the size of the list; the
list can grow to a larger size. We must know how full the array is.
2) Implement the list operations
· Variables needed to maintain and
process the list in an array
· The list can be sorted/ordered or unsorted/unordered - however,
the algorithms to implement certain operations are the same. Common operations
for the sorted/unsorted list are implemented in class ArrayListClass. The ArrayListClass is an abstract class (we do
not want to instantiate objects of this class) - it
does not implement all the operations of the interface ArrayListADT.
//Interface: ArrayListADT
//extends Cloneable
public interface ArrayListADT<T>
extends Cloneable {
public boolean isEmpty(); //Method to
determine whether the list is empty.
public boolean isFull(); //Method to
determine whether the list is full.
public int listSize(); //Method
to return the number of elements in the list.
public int maxListSize(); //Method to
return the maximum size of the list.
public void
print(); //Method to
output the elements of the list.
public Object clone(); //Returns a copy of objects data in store. Clones only
the references, not the objects
public boolean isItemAtEqual(int location, T item); //Method
to determine whether item is the same as the item in the list at location.
public void insertAt(int location, T insertItem); //Method
to insert insertItem in the list at the position
public void insertEnd(T
insertItem); //Method to
insert insertItem at the end of the list.
public void removeAt(int location); //Method to remove the item from the list at location.
public T retrieveAt(int
location); //Method to retrieve the
element from the list at location.
public void replaceAt(int location, T repItem); //Method to replace
the element in the list at location with repItem.
public void clearList(); //Method to
remove all the elements from the list.
public int search(T searchItem);
//Method to determine whether searchItem
is in the list.
public void
remove(T removeItem); //Method to remove an item from the list.
}
//Class:
ArrayListClass implements
//Interface:
ArrayListADT
public abstract class ArrayListClass<T> implements ArrayListADT<T>,
Cloneable {
protected int length; //to store the
length of the list
protected int maxSize; //to store the maximum size of the list
protected T[] list; //array to
hold the list elements
//Default constructor
public ArrayListClass() {
maxSize = 100;
length = 0;
list = (T[]) new Object[maxSize];
}
//Alternate Constructor
public ArrayListClass(int size) {
if(size <= 0) {
System.err.println("The array size must be
positive. Creating an array of size 100. ");
maxSize = 100;
}
else
maxSize = size;
length = 0;
list = (T[]) new Object[maxSize];
}
public boolean isEmpty()
{
return (length == 0);
}
public boolean isFull()
{
return (length == maxSize);
}
public int listSize()
{
return length;
}
public int maxListSize()
{
return maxSize;
}
public void print() {
for (int i = 0; i < length; i++)
System.out.print(list[i] +
" ");
System.out.println();
}
public Object clone() {
ArrayListClass<T> copy = null;
try {
copy = (ArrayListClass<T>) super.clone();
}
catch (CloneNotSupportedException e) {
return null;
}
copy.list = (T[]) list.clone();
return copy;
}
public boolean isItemAtEqual(int location, T item) {
if (location < 0 || location >= length) {
System.err.println("The location of the item to
be compared is out of range.");
return false;
}
return (list[location].equals(item));
}
public void clearList() {
for (int i = 0; i < length; i++)
list[i] = null;
length = 0;
System.gc(); //invoke
garbage collector
}
public void removeAt(int location) {
if (location < 0 || location >= length)
System.err.println("The location of the item to
be removed is out of range.");
else {
for(int i = location; i < length - 1; i++)
list[i] = list[i + 1];
list[length - 1] = null;
length--;
}
}
public T retrieveAt(int location) {
if (location < 0 || location >= length) {
System.err.println("The location of the item to
be retrieved is out of range.");
return null;
}
else
return list[location];
}
public abstract void insertAt(int
location, T insertItem);
public abstract void insertEnd(T insertItem);
public abstract void replaceAt(int
location, T repItem);
public abstract int search(T searchItem);
public abstract void remove(T removeItem);
}
//Class:
UnorderedArrayList extends
//Class:
ArrayListClass
public class UnorderedArrayList<T> extends ArrayListClass<T>
{
//Default constructor
public UnorderedArrayList() {
super();
}
//Alternate Constructor
public UnorderedArrayList(int size) {
super(size);
}
//Bubble Sort
public void bubbleSort() {
for (int pass = 0; pass < length - 1; pass++) {
for (int i = 0; i < length - 1; i++) {
Comparable<T> listElem
= (Comparable<T>) list[i];
if (listElem.compareTo(list[i
+ 1]) > 0) {
T temp = list[i];
list[i] = list[i + 1];
list[i + 1] = temp;
}
}
}
}
//implementation for abstract methods defined in ArrayListClass
//unordered list --> linear search
public int search(T searchItem) {
for(int i = 0; i < length; i++)
if(list[i].equals(searchItem))
return i;
return -1;
}
public void insertAt(int
location, T insertItem) {
if (location < 0 || location >= maxSize)
System.err.println("The position of the item to
be inserted is out of range.");
else if (length >= maxSize)
System.err.println("Cannot insert in a full
list.");
else {
for (int i = length; i > location; i--)
list[i] = list[i -
1]; //shift right
list[location] = insertItem;
length++;
}
}
public void insertEnd(T insertItem) {
if (length >= maxSize)
System.err.println("Cannot insert in a full
list.");
else {
list[length] = insertItem;
length++;
}
}
public void replaceAt(int location, T repItem) {
if (location < 0 || location >= length)
System.err.println("The location of the item to
be replaced is out of range.");
else
list[location] = repItem;
}
public void remove(T removeItem) {
int i;
if (length == 0)
System.err.println("Cannot delete from an empty
list.");
else {
i = search(removeItem);
if (i != -1)
removeAt(i);
else
System.out.println("Cannot delete! The item to
be deleted is not in the list.");
}
}
}
//Class:
ClientUnorderedListInt
//Client
program to test the UnorderedList with Integer
objects
import java.util.Scanner;
public class ClientUnorderedListInt {
public static final int SIZE = 20;
public
static void main(String[] args) {
Scanner input = new Scanner(System.in);
UnorderedArrayList<Integer> list = new UnorderedArrayList<Integer>(SIZE);
UnorderedArrayList<Integer> list2 = new UnorderedArrayList<Integer>(SIZE);
Integer n;
int index;
list.insertEnd(200);
list.insertEnd(15);
list.insertEnd(3);
list.insertEnd(10);
list.insertEnd(100);
list.insertEnd(37);
System.out.println("Testing .insertEnd.
Inserted in the list values: 200 15 3 10 100 37");
System.out.println("The original list is: ");
list.print();
System.out.print("Testing .search. Enter value
to search for: ");
n = input.nextInt(); //Change to getInt()
for type check
index = list.search(n);
if(index != -1)
System.out.println("Found " + n + " in
the element with index " + index);
else
System.out.println(n + " not found in this
list");
System.out.print("Testing .remove. Enter value
to remove from list: ");
n = input.nextInt();//Change to getInt()
for type check
list.remove(n);
System.out.println("The list after removing
" + n + " is: ");
list.print();
list2 = copyList(list);
System.out.println("Testing client method copyList. The copy list (list2) is: ");
list2.print();
n = list2.retrieveAt(0);
System.out.println("Testing .retrieveAt.
First element in list2 is: " + n);
list2.replaceAt(0, 25);
System.out.println("Testing .replaceAt.
Changed the first element in list2 to 25. ");
System.out.println("After change, list2 is: ");
list2.print();
System.out.println("Was the original list
changed? If not, list2 is a deep copy! The original list is: ");
list.print();
System.out.println("Testing .bubbleSort.
The original list sortd is: ");
list.bubbleSort();
list.print();
}
public static UnorderedArrayList<Integer>
copyList (UnorderedArrayList<Integer>
otherList) {
UnorderedArrayList<Integer> tempList
= new UnorderedArrayList<Integer>(otherList.maxListSize());
Integer n;
for (int i = 0; i < otherList.listSize(); i++) {
n = otherList.retrieveAt(i);
tempList.insertEnd(n);
}
return tempList;
}
//Add method getInt()
}
OUTPUT:
Testing .insertEnd. Inserted in the list values: 200 15 3 10 100 37
The original list is:
200
15 3 10 100 37
Testing .search. Enter
value to search for: 100
Found 100 in the
element with index 4
Testing .remove. Enter
value to remove from list: 15
The list after
removing 15 is:
200
3 10 100 37
Testing client method copyList. The copy list (list2) is:
200
3 10 100 37
Testing .retrieveAt. First element in list2 is:
200
Testing .replaceAt. Changed the first element in list2 to 25.
After change, list2
is:
25
3 10 100 37
Was the original list
changed? If not, list2 is a deep copy! The original list is:
200
3 10 100 37
Testing .bubbleSort. The original list sortd
is:
3
10 37 100 200
//Class:
ClientUnorderedListTime
//Client
program to test the UnorderedList with Time objects
public class ClientUnorderedListTime {
public static final int SIZE = 20;
public static void main(String[] args) {
UnorderedArrayList<Time> timeList
= new UnorderedArrayList<Time>(SIZE);
UnorderedArrayList<Time> temp1 = new UnorderedArrayList<Time>(SIZE);
UnorderedArrayList<Time> temp2 = new UnorderedArrayList<Time>(SIZE);
timeList.insertEnd(new Time(1, 2, 3));
timeList.insertEnd(new Time(4, 5, 6));
timeList.insertEnd(new Time(7, 8, 9));
System.out.println("The original list is:
");
timeList.print();
temp1 = (UnorderedArrayList<Time>)
timeList.clone();
System.out.println("The copy list (temp1) after
call to clone: ");
temp1.print();
temp2 = copyList(timeList);
System.out.println("The copy list (temp2) after
call to copyList: ");
temp2.print();
Time tl;
tl = temp1.retrieveAt(0);
tl.setTime(11, 12, 13);
System.out.println("Changed the first element in
temp1 to 11:12:13");
System.out.println("After change, temp1 is:
");
temp1.print();
System.out.println("Was the original list
changed? If yes, temp1 is a shallow copy! The original list is: ");
timeList.print();
System.out.println("Was temp2 changed? If not,
temp2 is a deep copy. temp2 is: ");
temp2.print();
}
public static UnorderedArrayList<Time> copyList (UnorderedArrayList<Time>
otherList) {
UnorderedArrayList<Time> tempList
= new UnorderedArrayList<Time>(otherList.maxListSize());
Time tl = new Time();
for (int i = 0; i < otherList.listSize(); i++) {
tl = otherList.retrieveAt(i);
tempList.insertEnd((Time) tl.clone());
}
return tempList;
}
}
OUTPUT:
The original list is:
01:02:03
04:05:06 07:08:09
The copy list (temp1)
after call to clone:
01:02:03
04:05:06 07:08:09
The copy list (temp2)
after call to copyList:
01:02:03
04:05:06 07:08:09
Changed the first element
in temp1 to 11:12:13
After change, temp1
is:
11:12:13
04:05:06 07:08:09
Was the original list
changed? If yes, temp1 is a shallow copy! The original list is:
11:12:13 04:05:06 07:08:09
Was temp2 changed? If
not, temp2 is a deep copy. temp2 is:
01:02:03
04:05:06 07:08:09
//Class:
OrderedArrayList extends
//Class:
ArrayListClass
public class OrderedArrayList<T> extends ArrayListClass<T>{
//Default constructor
public OrderedArrayList() {
super();
}
//Alternate constructor
public OrderedArrayList(int size) {
super(size);
}
//implementation for abstract methods defined in ArrayListClass
//ordered list --> binary search
public int search(T item) {
int first = 0;
int last = length - 1;
int middle = -1;
while (first <= last) {
middle = (first + last) / 2;
Comparable<T> listElem = (Comparable<T>)
list[middle];
if (listElem.compareTo(item) == 0)
return middle;
else
if (listElem.compareTo(item) > 0)
last = middle - 1;
else
first = middle + 1;
}
return -1;
}
public void insert(T item) {
int loc;
boolean found = false;
if (length == 0) //list is empty
list[length++] = item; //insert item and
increment length
else if (length == maxSize) //list
is full
System.err.println("Cannot insert in a full
list.");
else {
for (loc = 0; loc <
length; loc++) {
Comparable<T> temp = (Comparable<T>) list[loc];
if (temp.compareTo(item) >= 0) {
found = true;
break;
}
}
//starting at the end, shift right
for (int i = length; i > loc; i--)
list[i] = list[i - 1];
list[loc] = item;
length++;
}
}
/* Another version for insert:
public
void insert(T item) {
int loc;
boolean found = false;
if (length ==
0) //list is
empty
list[length++] = item; //insert item and increment length
else if (length == maxSize) //list is full
System.err.println("Cannot insert in a full
list.");
else {
int i = length - 1;
//while (i >= 0 && list[i] > item) {
while (i >= 0 && ((Comparable<T>)
list[i]).compareTo(item)
> 0) {
list[i + 1] = list[i];
i--;
}
list[i + 1] = item; //
Insert item
length++;
}
} */
public void insertAt(int location, T item) {
if (location < 0 || location >= maxSize)
System.err.println("The position of the item to
be inserted is out of range.");
else if (length == maxSize) //list is full
System.err.println("Cannot insert in a full
list.");
else {
System.out.println("This is a sorted list. Doing
insert in place (call to insert).");
insert(item);
}
}
public void insertEnd(T item) {
if (length == maxSize) //the list is full
System.err.println("Cannot insert in a full
list.");
else {
System.out.println("This is a sorted list. Doing
insert in place (call to insert).");
insert(item);
}
}
public void replaceAt(int location, T item) {
//the list is sorted!
//is actually removing the element at location and inserting item in place
if (location < 0 || location >= length)
System.err.println("The position of the item to be replaced is out of
range.");
else {
removeAt(location);//method
in ArrayListClass
insert(item);
}
}
public void remove(T item) {
int loc;
if (length == 0)
System.err.println("Cannot delete from an empty
list.");
else {
loc = search(item);
if (loc != -1)
removeAt(loc);//method in ArrayListClass
else
System.out.println("The item to be deleted is
not in the list.");
}
}
/*Another version for remove:
public void remove(T item) {
int loc;
if (length == 0)
System.err.println("Cannot delete from an empty
list.");
else {
loc = search(item);
if (loc != -1) {
for(int i = loc; i < length - 1; i++)
list[i] = list[i + 1];
//shift left
length--;
}
else
System.out.println("The item to be deleted is
not in the list.");
}
} */
}
//Class:
ClientUnorderedListInt
//Client
program to test the UnorderedList with Integer
objects
import java.util.Scanner;
public class ClientOrderedListInt {
public static final int SIZE = 20;
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
OrderedArrayList<Integer> list = new OrderedArrayList<Integer>(SIZE);
OrderedArrayList<Integer> list2 = new OrderedArrayList<Integer>(SIZE);;
Integer n;
int index;
list.insert(5);
list.insert(3);
list.insert(10);
list.insert(100);
list.insert(37);
System.out.println("Testing .insert. Inserted in
the list the values: 5 3 10 100 37");
System.out.println("The original list is: ");
list.print();
System.out.print("Testing .search. Enter value
to search for: ");
n = input.nextInt(); //Change to getInt()
for type check
index = list.search(n);
if(index != -1)
System.out.println("Found " + n + " in
the element with index " + index);
else
System.out.println(n + " not found in this
list");
System.out.print("Testing .remove. Enter value
to remove from list: ");
n = input.nextInt(); //Change to getInt() for type
check
list.remove(n);
System.out.println("The list after removing
" + n + " is: ");
list.print();
list2 = copyList(list);
System.out.println("Testing client method copyList. The copy list (list2) is: ");
list2.print();
n = list2.retrieveAt(0);
System.out.println("Testing .retrieveAt.
First element in list2 is: " + n);
list2.replaceAt(0, 25);
System.out.println("Testing .replaceAt.
Removed first element in list2, added value 25. ");
System.out.println("After change, list2 is: ");
list2.print();
System.out.println("Was the original list
changed? If not, list2 is a deep copy! The original list is: ");
list.print();
}
public static OrderedArrayList<Integer>
copyList (OrderedArrayList<Integer>
otherList) {
OrderedArrayList<Integer> tempList
= new OrderedArrayList<Integer>(otherList.maxListSize());
Integer n;
for (int i = 0; i < otherList.listSize(); i++) {
n = otherList.retrieveAt(i);
tempList.insert(n);
}
return tempList;
}
//Add method getInt()
}
OUTPUT:
Testing .insert.
Inserted in the list the values: 5 3 10 100 37
The original list is:
3
5 10 37 100
Testing .search. Enter
value to search for: 37
Found 37 in the
element with index 3
Testing .remove. Enter
value to remove from list: 5
The list after
removing 5 is:
3
10 37 100
Testing client method copyList. The copy list (list2) is:
3
10 37 100
Testing .retrieveAt. First element in list2 is:
3
Testing .replaceAt. Removed first element in list2, added value 25.
After change, list2
is:
10
25 37 100
Was the original list
changed? If not, list2 is a deep copy! The original list is:
3
10 37 100
//Class:
ClientOrderedListTime
//Client
program to test the OrderedList with Time objects
import java.util.Scanner;
public class ClientOrderedListTime {
public static final int SIZE = 20;
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int h, m, s;
OrderedArrayList<Time> timeList
= new OrderedArrayList<Time>(SIZE);
OrderedArrayList<Time> temp1 = new OrderedArrayList<Time>(SIZE);
OrderedArrayList<Time> temp2 = new OrderedArrayList<Time>(SIZE);
timeList.insert(new Time(1, 2, 3));
timeList.insert(new Time(11, 22, 33));
timeList.insert(new Time(1, 12, 13));
timeList.insert(new Time(4, 5, 6));
timeList.insert(new Time(11, 12, 13));
timeList.insert(new Time(7, 8, 9));
System.out.println("Testing .insert. The original list is: ");
timeList.print();
System.out.println("Testing .listSize.
The size of the list is: " + timeList.listSize());
temp1 = (OrderedArrayList<Time>) timeList.clone();
System.out.println("Testing .clone. The copy
list (temp1) is: ");
temp1.print();
temp2 = copyList(timeList);
System.out.println("Testing client method copyList. The copy list (temp2) is: ");
temp2.print();
Time t = new Time();
t.setTime(11, 12, 14);
temp1.insert(t);
System.out.println("Testing .insert. The copy
list (temp1) is: ");
temp1.print();
System.out.println("Testing .remove. The copy
list (temp1) is: ");
temp1.remove(t);
temp1.print();
t = temp1.retrieveAt(3);
System.out.println("Testing .remove. The copy
list (temp1) is: ");
temp1.remove(t);
temp1.print();
System.out.print("Enter hours minutes and
seconds: ");
h = input.nextInt();//Change to getInt()
for type check
m = input.nextInt();//Change to getInt()
for type check
s = input.nextInt();//Change to getInt()
for type check
t = new Time(h, m, s);
if (timeList.search(t) != -1)
System.out.println("Testing .search. The time " + t + " found in original list.");
else
System.out.println("Testing .search. The time " + t + " NOT found in original list.");
System.out.println("The original list is:
");
timeList.print();
System.out.println("The copy list (temp2) is:
");
temp2.print();
}
public static OrderedArrayList<Time> copyList (OrderedArrayList<Time>
otherList) {
OrderedArrayList<Time> tempList
= new OrderedArrayList<Time>(otherList.maxListSize());
Time tl = new Time();
for (int i = 0; i < otherList.listSize(); i++) {
tl = otherList.retrieveAt(i);
tempList.insert((Time) tl.clone());
}
return tempList;
}
//Add method getInt()
}
OUTPUT:
Testing .insert. The
original list is:
01:02:03 01:12:13 04:05:06 07:08:09
11:12:13 11:22:33
Testing .listSize. The size of the list is:
6
Testing .clone. The
copy list (temp1) is:
01:02:03 01:12:13 04:05:06 07:08:09
11:12:13 11:22:33
Testing client method copyList. The copy list (temp2) is:
01:02:03 01:12:13 04:05:06 07:08:09
11:12:13 11:22:33
Testing .insert. The
copy list (temp1) is:
01:02:03 01:12:13 04:05:06 07:08:09
11:12:13 11:12:14 11:22:33
Testing .remove. The
copy list (temp1) is:
01:02:03 01:12:13 04:05:06 07:08:09
11:12:13 11:22:33
Testing .remove. The
copy list (temp1) is:
01:02:03 01:12:13 04:05:06 11:12:13 11:22:33
Enter hours minutes
and seconds: 4 5 6
Testing .search. The
time 04:05:06 found in original list.
The original list is:
01:02:03
01:12:13 04:05:06 07:08:09 11:12:13 11:22:33
The copy list (temp2)
is:
01:02:03
01:12:13 04:05:06 07:08:09 11:12:13 11:22:33
· Although arrays are conceptually important as a data structure, they
are not used as much in Java as they are in most other languages. The
reason is that the java.util package includes a class
called ArrayList that provides the standard
array behavior along with other useful operations.
· ArrayList is a class in the standard
Java libraries that can hold any type of object --> In general, an ArrayList serves the same purpose as
an array, except that an ArrayList can change length while the
program is running (unlike arrays, which have a fixed length once they have
been created).
· The type you specify when creating an ArrayList must be an object type; it
cannot be a primitive type --> must use wrapper classes!
· Each object of the ArrayList class has a capacity. The
capacity is the size of the array used to store the elements in the list (it is
always at least as large as the list size.) As elements are added to an ArrayList, its capacity grows
automatically.
· The main difference between Java arrays and ArrayList --> ArrayList is a Java class rather than
a special data type in the language. As a result, all operations on ArrayLists are indicated using method
calls. For example, the most obvious differences include:
· Why use an array instead of an ArrayList:
· Why use an ArrayList instead of an array?
· NOTE: In order to make use of the ArrayList
class, must
add: import java.util.ArrayList;
· NOTE: The Java standard libraries
have a class named Vector that behaves almost exactly the same as the class ArrayList. In most situations, either
class could be used, however the ArrayList class is newer (Java 5), and
is becoming the preferred class.
· Some methods in the ArrayList class:
Much
more in detail (source:http://java.sun.com/javase/6/docs/api/
) a more extensive list of methods for the ArrayList class (using generics):
boolean add(E e) -->
Appends the specified element to the end of this list.
void add(int index, E element)
--> Inserts the specified element at the specified position in
this list.
boolean addAll(Collection<?
extends E> c) --> Appends all of the elements in the specified
collection to the end of this list, in the order that they are returned by the
specified collection's Iterator.
boolean addAll(int index, Collection<? extends E> c) -->
Inserts all of the elements in the specified collection into this list,
starting at the specified position.
void clear() --> Removes all of the elements
from this list.
Object clone() --> Returns a shallow copy of this ArrayList instance.
boolean contains(Object o) -->
Returns true if this list contains the specified element.
void ensureCapacity(int minCapacity) -->
Increases the capacity of this ArrayList instance, if
necessary, to ensure that it can hold at least the number of elements specified
by the minimum capacity argument.
E get(int
index) --> Returns the element at the specified position
in this list.
int indexOf(Object
o) --> Returns the index of the first occurrence of the
specified element in this list, or -1 if this list does not contain the
element.
boolean isEmpty()
--> Returns true if this list contains no elements.
int lastIndexOf(Object
o) --> Returns the index of the last occurrence of the
specified element in this list, or -1 if this list does not contain the
element.
E remove(int index) --> Removes
the element at the specified position in this list.
boolean remove(Object o) --> Removes
the first occurrence of the specified element from this list, if it is present.
protected void removeRange(int fromIndex, int toIndex) --> Removes
from this list all of the elements whose index is between fromIndex,
inclusive, and toIndex, exclusive.
E set(int index, E element) --> Replaces
the element at the specified position in this list with the specified element.
int size() --> Returns
the number of elements in this list.
Object[] toArray() --> Returns
an array containing all of the elements in this list in proper sequence (from
first to last element).
<T> T[] toArray(T[] a) --> Returns
an array containing all of the elements in this list in proper sequence (from
first to last element); the runtime type of the returned array is that of the
specified array.
void trimToSize() --> Trims
the capacity of this ArrayList
· NOTE: When looking at the methods
available in the ArrayList class, there appears to be
some inconsistency - in some cases, when a parameter is naturally an object of
the base type, the parameter type is the base type; however, in other cases, it
is the type Object. Why? Because the ArrayList class implements a number of
interfaces, and inherits methods from various superclasses
- they specify that certain parameters have type Object.
· NOTE: The ArrayList class is an example of a
collection class (to be discussed later). Starting with version 5.0, Java has
added a new kind of for loop called a for-each
or enhanced for loop. This kind of loop has been designed to cycle
through all the elements in a collection (like an ArrayList).
· Example #1:
import java.util.ArrayList;
public class ExampleForEach
implements Cloneable{
public static void main(String[ ] args){
ArrayList<Integer> list = new ArrayList<Integer>();
ArrayList<Integer> copyList
= new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);
System.out.println("The original list:");
//Reads like: "for each Integer i, in list"
for(Integer
i:list)
System.out.print(i + "
");
copyList = (ArrayList)list.clone();
for(int i = 0; i
< copyList.size( ); i++)
copyList.set(i, new
Integer(list.get(i)));
System.out.println("\nThe
clone list:");
//Reads like: "for each Integer i, in copyList"
for(Integer
i:copyList)
System.out.print(i + "
");
System.out.println();
}
}
Output:
The original list:
1 2 3
The clone list:
1 2 3
· Example #2:
import java.util.ArrayList;
public class ExampleArrayList
implements Cloneable{
public static void main( String[ ] args) {
ArrayList<Integer> list = new ArrayList<Integer>();
//initial capacity = 10
ArrayList<Integer> copyList
= new ArrayList<Integer>(); //initial capacity = 10
System.out.println("Size of original(empty) list =
" + list.size());
for (int i = 1; i
<= 10; i++)
list.add(2 * i);
System.out.println("Added 10 values to list. The new
size is: " + list.size());
System.out.println("The list is " + list);
list.set(0, 59);
System.out.println("Changed the element with index 0
to 59.");
System.out.println("The new list is " + list);
list.add(3, 37);
System.out.println("Added 37 at index 3. Increased
capacity! The new size is: " + list.size());
System.out.println("The new list is " + list);
list.remove(6);
System.out.println("Removed element with index 6. The
new size is: " + list.size());
System.out.println("The new list is " + list);
list.remove((Integer)(6));
System.out.println("Removed the value 6. The new size
is: " + list.size());
System.out.println("The new list is " + list);
System.out.println("Printing the list using .get/for
loop. The list is: ");
for (int i = 0; i
< list.size(); i++)
System.out.print(list.get(i) + " " );
if (list.contains(10))
System.out.println("\nLooked
for value 10 / list. 10 found at index " + list.indexOf(10));
else
System.out.println("Looked for 10/list. 10 NOT
found.");
copyList = (ArrayList)list.clone(); //shallow copy
//make a deep
copy
for(int i = 0; i
< copyList.size( ); i++)
copyList.set(i, new
Integer(list.get(i)));
System.out.println("\nThe
clone list (using for each):");
for(Integer
i:copyList)
System.out.print(i + "
");
System.out.println("\nThe
clone list (using toString: \n" + copyList);
System.out.println();
}
}
OUTPUT:
Size of original(empty) list = 0
Added 10 values to list. The new size is: 10
The
list is [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
Changed the element with index 0 to 59.
The new list is [59, 4, 6, 8, 10, 12, 14, 16, 18, 20]
Added 37 at index 3. Increased capacity! The new size is: 11
The new list is [59, 4, 6, 37, 8, 10, 12, 14, 16, 18, 20]
Removed element with index 6. The new size is: 10
The
new list is [59, 4, 6, 37, 8, 10, 14, 16, 18, 20]
Removed the value 6. The new size is:
9
The new list is [59, 4, 37, 8, 10, 14, 16, 18, 20]
Printing the list using .get/for loop. The list is:
59 4 37 8 10 14 16 18 20
Looked for value 10 / list. 10 found at index 4
The clone list
(using for each):
59 4 37 8 10 14 16 18
20
The clone list (using toString:
[59, 4, 37, 8, 10, 14,
16, 18, 20]
Key Terms
ADT: A data type that specifies the
logical properties without the implementation details (information hiding)
Clone method: A method that provides
a bit-by-bit copy of the object’s data in storage (shallow copy of object’s
data).
Cloneable: An interface that forces a class to provide
an appropriate definition of the method clone.
Comparable: An interface used to
force a class to provide an appropriate definition of the method compareTo so that the values of two
objects of that class can be properly compared.
Generic classes (parametric classes):
Classes that are used to write a single definition for a set of related
classes. Defined using type parameter.
Generic method: Method defined using
type parameter.
List: A linear collection of elements
of the same type.
(List) Length: The number of elements
in the list.
Ordered list: An ordered collection
of elements of the same type. A list in which data items are placed in ascending
(or descending) order.
Set: A list with distinct elements.
Type parameters (type
variables): Identifiers that specify generic type names.
Unordered list: An unordered
collection of elements of the same type. A list in which data items are placed
in no particular order.
Wrapper class: A class that
allows a primitive data type to be instantiated as an object.
Additional
Resources:
1. (Oracle/Sun) API specification for version 6 of the Java Platform, Standard
Edition (Cloneable,
Comparable, ArrayList): http://docs.oracle.com/javase/6/docs/api/
2. (Oracle/Sun) The Java Tutorials, Generics in the Java Programming Language
(Gilad Bracha): https://docs.oracle.com/javase/tutorial/extra/generics/
3. (Oracle/Sun) The Java Tutorials, Generics: http://docs.oracle.com/javase/tutorial/java/generics/index.html
4. Java Generics FAQs: http://www.angelikalanger.com/GenericsFAQ/JavaGenericsFAQ.html
References:
[1] Java Programming: From Problem Analysis to Program Design, by D.S. Malik,
Thomson Course Technology, 2008
[2] Building Java Programs: A Back to Basics Approach, by Stuart Reges, and Marty Stepp, Addison
Wesley, 2008.