1. Chapter 10 Arrays Animated Version
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2. Intro to OOP with Java, C. Thomas Wu
Objectives
After you have read and studied this chapter, you should be able to
Manipulate a collection of data values, using an array.
Declare and use an array of primitive data types in writing a program.
Declare and use an array of objects in writing a program
Define a method that accepts an array as its parameter and a method that returns an array
Describe how a two-dimensional array is implemented as an array of arrays
Manipulate a collection of objects, using lists and maps
We will cover the basic array processing in this lesson, manipulating arrays of primitive data types and objects.
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3. Intro to OOP with Java, C. Thomas Wu
Array Basics
An array is a collection of data values.
If your program needs to deal with 100 integers, 500 Account objects, 365 real numbers, etc., you will use an array.
In Java, an array is an indexed collection of data values of the same type.
Suppose you need to handle up to 300 Student objects in a program for maintaining a high school alumni list, would you use 300 variables?
Suppose you need to process daily temperatures for a 12-month period in a science project, would you use 365 variables?
You can, but would you? To manipulate a collection of data, we can use arrays.
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4. Arrays of Primitive Data Types
Intro to OOP with Java, C. Thomas Wu
Arrays of Primitive Data Types
Array Declaration
<data type> [ ] <variable> //variation 1
<data type> <variable>[ ] //variation 2
Array Creation
<variable> = new <data type> [ <size> ]
Example
double[ ] rainfall;
rainfall
= new double[12];
Variation 1
double rainfall [ ];
rainfall
= new double[12];
Variation 2
As you can declare and create objects in one statement such as
Person p = new Person( );
you can declare and create an array in one statement as
double[ ] rainfall = new double[12];
Strictly speaking, an array is a reference data type and really an object because there is no class called Array in Java. The thumbnail note in page 413 is therefore not 100 percent accurate.
An array is like an object!
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5. Accessing Individual Elements
Intro to OOP with Java, C. Thomas Wu
Accessing Individual Elements
Individual elements in an array accessed with the indexed expression.
double[] rainfall = new double[12];
rainfall 1 2 3 4 5 6 7 8 9 10 11
rainfall[2]
This indexed expression refers to the element at position #2
The index of the first
position in an array is 0.
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6. Array Processing – Sample1
Intro to OOP with Java, C. Thomas Wu
Array Processing – Sample1
double[] rainfall = new double[12];
double annualAverage,
sum = 0.0;
for (int i = 0; i < rainfall.length; i++) {
rainfall[i] = Double.parseDouble(
JOptionPane.showinputDialog(null,
"Rainfall for month " + (i+1) ) );
sum += rainfall[i]; }
annualAverage = sum / rainfall.length;
The public constant length returns the capacity of an array.
This code computes the average annual rainfall. Notice the public constant length returns the capacity, not the actual number of non-blank values in the array.
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7. Array Processing – Sample 2
Intro to OOP with Java, C. Thomas Wu
Array Processing – Sample 2
double[] rainfall = new double[12];
String[] monthName = new String[12];
monthName[0] = "January";
monthName[1] = "February"; …
double annualAverage, sum = 0.0;
for (int i = 0; i < rainfall.length; i++) {
rainfall[i] = Double.parseDouble(
JOptionPane.showinputDialog(null, "Rainfall for " monthName[i] ));
sum += rainfall[i]; }
annualAverage = sum / rainfall.length;
The same pattern for the remaining ten months.
This code also computes the average annual rainfall, but this time we use the second array, an arrray of String so the prompt becomes "Rainfall for January", "Rainfall for February", and so forth. Notice how the monthName array is used in the for loop.
The actual month name instead of a number.
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8. Array Processing – Sample 3
Intro to OOP with Java, C. Thomas Wu
Array Processing – Sample 3
Compute the average rainfall for each quarter.
//assume rainfall is declared and initialized properly
double[] quarterAverage = new double[4];
for (int i = 0; i < 4; i++) {
sum = 0;
for (int j = 0; j < 3; j++) { //compute the sum of
sum += rainfall[3*i + j]; //one quarter }
quarterAverage[i] = sum / 3.0; //Quarter (i+1) average
This code computes the average rainfall for each quarter. The inner loop is used to compute the rainfall for a given quarter. The outer loop processes the four quarters.
This is how the values
for i, j, and 3*i+j change:
i j 3*i+j
0 0 0
1 1
2 2
1 0 3
1 4
2 5
2 0 6
1 7
2 8
1 10
2 11
The sample code is equivalent to
for (int i = 0; i < 3; i++ ) {
quarterAverage[0] += rainfall[i];
quarterAverage[1] += rainfall[i+3];
quarterAverage[2] += rainfall[i+6];
quarterAverage[3] += rainfall[i+9]; }
quarterAverage[0] = quarterAverage[0] / 3.0;
quarterAverage[1] = quarterAverage[1] / 3.0;
quarterAverage[2] = quarterAverage[2] / 3.0;
quarterAverage[3] = quarterAverage[3] / 3.0;
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9. Intro to OOP with Java, C. Thomas Wu
Array Initialization
Like other data types, it is possible to declare and initialize an array at the same time.
int[] number = { 2, 4, 6, 8 };
double[] samplingData = { 2.443, 8.99, 12.3, , 18.2,
9.00, 3.123, , };
String[] monthName = { "January", "February", "March",
"April", "May", "June", "July",
"August", "September", "October",
"November", "December" };
When an array is initialized in this manner, its capacity is set to the number of elements in the list.
number.length samplingData.length monthName.length 4 9 12
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10. Variable-size Declaration
Intro to OOP with Java, C. Thomas Wu
Variable-size Declaration
In Java, we are not limited to fixed-size array declaration.
The following code prompts the user for the size of an array and declares an array of designated size:
int size;
int[] number;
size= Integer.parseInt(JOptionPane.showInputDialog(null,
"Size of an array:"));
number = new int[size];
Instead of declaring the array size to a fixed value, it is possible to declare its size at the runtime. For example, we can prompt the user for the size of an array as illustrated in the sample code shown here.
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11. Intro to OOP with Java, C. Thomas Wu
Arrays of Objects
In Java, in addition to arrays of primitive data types, we can declare arrays of objects
An array of primitive data is a powerful tool, but an array of objects is even more powerful.
The use of an array of objects allows us to model the application more cleanly and logically.
By combining the power of arrays and objects, we can structure programs in a clean, logical manner.
Without an array of objects, to represent a collection of Account objects, for example, we need to use several different arrays, one for names, one for addresses, and so forth. This is very cumbersome and error-prone.
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12. Intro to OOP with Java, C. Thomas Wu
The Person Class
We will use Person objects to illustrate the use of an array of objects.
Person latte;
latte = new Person( );
latte.setName("Ms. Latte");
latte.setAge(20);
latte.setGender('F');
System.out.println( "Name: " + latte.getName() );
System.out.println( "Age : " + latte.getAge() );
System.out.println( "Sex : " + latte.getGender() );
The Person class supports the set methods and get methods.
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13. Creating an Object Array - 1
Intro to OOP with Java, C. Thomas Wu
Creating an Object Array - 1
Code
Person[ ] person;
person = new Person[20];
person[0] = new Person( ); A
Only the name person is declared, no array is allocated yet.
After is executed A
person
State of
Memory
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14. Creating an Object Array - 2
Intro to OOP with Java, C. Thomas Wu
Creating an Object Array - 2
Code
Person[ ] person;
person = new Person[20];
person[0] = new Person( );
Now the array for storing 20 Person objects is created, but the Person objects themselves are not yet created. B
person
After is executed B 1 2 3 4 16 17 18 19
person
State of
Memory
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15. Creating an Object Array - 3
Intro to OOP with Java, C. Thomas Wu
Creating an Object Array - 3
Code
Person[ ] person;
person = new Person[20];
person[0] = new Person( );
One Person object is created and the reference to this object is placed in position 0. C 1 2 3 4 16 17 18 19
person 1 2 3 4 16 17 18 19
person
After is executed C
Person
State of
Memory
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16. Person Array Processing – Sample 1
Intro to OOP with Java, C. Thomas Wu
Person Array Processing – Sample 1
Create Person objects and set up the person array.
String name, inpStr;
int age;
char gender;
for (int i = 0; i < person.length; i++) {
name = inputBox.getString("Enter name:"); //read in data values
age = inputBox.getInteger("Enter age:");
inpStr = inputBox.getString("Enter gender:");
gender = inpStr.charAt(0);
person[i] = new Person( ); //create a new Person and assign values
person[i].setName ( name );
person[i].setAge ( age );
person[i].setGender( gender ); }
The indexed expression
person[i]
is used to refer to the (i+1)st object in the person array. Since this expression refers to an object, we write
person[i].setAge( 20 );
to call this Person object’s setAge method, for example. This is the syntax we use to call an object’s method. We are just using an indexed expression to refer to an object instead of a simple variable.
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17. Person Array Processing – Sample 2
Intro to OOP with Java, C. Thomas Wu
Person Array Processing – Sample 2
Find the youngest and oldest persons.
int minIdx = 0; //index to the youngest person
int maxIdx = 0; //index to the oldest person
for (int i = 1; i < person.length; i++) {
if ( person[i].getAge() < person[minIdx].getAge() ) {
minIdx = i; //found a younger person
} else if (person[i].getAge() > person[maxIdx].getAge() ) {
maxIdx = i; //found an older person }
//person[minIdx] is the youngest and person[maxIdx] is the oldest
Here’s another approach with two Person variables:
Person youngest, //points to the youngest person
oldest; //points to the oldest person
youngest = oldest = person[0];
for (int i = 1; i < person.length; i++) {
if ( person[i].getAge() < youngest.getAge() ) {
youngest = person[i]; //found a younger person }
else if ( person[i].getAge() > oldest.getAge() ) {
oldest = person[i]; //found an older person
outputBox.printLine("Oldest : " + oldest.getName()
+ " is " + oldest.getAge() + " years old.");
outputBox.printLine("Youngest: " + youngest.getName()
+ " is " + youngest.getAge() + " years old.");
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18. Object Deletion – Approach 1
Intro to OOP with Java, C. Thomas Wu
Object Deletion – Approach 1
int delIdx = 1;
person[delIdx] = null;
Delete Person B by setting the reference in position 1 to null. A 1 2 3
person A B C D 1 2 3
person A C D
Before is executed
After is executed
In this approach, we simply leave the position of a deleted object to a null. With this approach, an array index positions will be a mixture of null and real pointers.
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19. Object Deletion – Approach 2
Intro to OOP with Java, C. Thomas Wu
Object Deletion – Approach 2
int delIdx = 1, last = 3;
person[delIndex] = person[last];
person[last] = null;
Delete Person B by setting the reference in position 1 to the last person. A 1 2 3
person A B C D 1 2 3
person A C D
Before is executed
After is executed
With the second approach, we divide the array into two parts: the first part contains the real
references and the second part contains the null references. When we delete a node, a hole will result and we must fill this hole.
There are two possible solutions. The first solution is to pack the elements. If an object at position J is removed (i.e., this position is set to null), then elements from position J+1 till the last non-null reference are shifted one position lower. And, finally, the last non-null reference is set to null. The second solution is to replace the removed element by the last element in the array. The first solution is necessary if the Person objects are arranged in some order (e.g., in ascending order of age). The second solution is a better one if the Person objects are not arranged in any order.
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20. Person Array Processing – Sample 3
Intro to OOP with Java, C. Thomas Wu
Person Array Processing – Sample 3
Searching for a particular person. Approach 2 Deletion is used.
int i = 0;
while ( person[i] != null && !person[i].getName().equals("Latte") ) {
i++; }
if ( person[i] == null ) {
//not found - unsuccessful search
System.out.println("Ms. Latte was not in the array");
} else {
//found - successful search
System.out.println("Found Ms. Latte at position " + i);
Here’s another approach with two Person variables:
Person youngest, //points to the youngest person
oldest; //points to the oldest person
youngest = oldest = person[0];
for (int i = 1; i < person.length; i++) {
if ( person[i].getAge() < youngest.getAge() ) {
youngest = person[i]; //found a younger person }
else if ( person[i].getAge() > oldest.getAge() ) {
oldest = person[i]; //found an older person
System.out.println("Oldest : " + oldest.getName()
+ " is " + oldest.getAge() + " years old.");
System.out.println("Youngest: " + youngest.getName()
+ " is " + youngest.getAge() + " years old.");
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21. Passing Arrays to Methods - 1
Intro to OOP with Java, C. Thomas Wu
Passing Arrays to Methods - 1
Code A
public int searchMinimum(float[] number)) { … }
minOne
= searchMinimum(arrayOne);
At before searchMinimum A
arrayOne
A. Local variable number does not exist before the method execution
When an array is passed to a method, only its reference is passed. A copy of the array is NOT created in the method.
public int searchMinimum(float[] number) {
int indexOfMinimum = 0;
for (int i = 1; i < number.length; i++) {
if (number[i] < number[indexOfMinimum]) { //found a
indexOfMinimum = i; //smaller element }
return indexOfMinimum;
State of Memory
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22. Passing Arrays to Methods - 2
Intro to OOP with Java, C. Thomas Wu
Passing Arrays to Methods - 2
Code
public int searchMinimum(float[] number)) { … } B
minOne
= searchMinimum(arrayOne);
arrayOne
The address is copied at B
number
arrayOne
B. The value of the argument, which is an address, is copied to the parameter.
State of Memory
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23. Passing Arrays to Methods - 3
Intro to OOP with Java, C. Thomas Wu
Passing Arrays to Methods - 3
Code
public int searchMinimum(float[] number)) { … } C
minOne
= searchMinimum(arrayOne);
arrayOne
number
While at inside the method C
C. The array is accessed via number inside the method.
State of Memory
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24. Passing Arrays to Methods - 4
Intro to OOP with Java, C. Thomas Wu
Passing Arrays to Methods - 4
Code
public int searchMinimum(float[] number)) { … }
minOne
= searchMinimum(arrayOne); D
arrayOne
At after searchMinimum D
arrayOne
At after searchMinimum D
number
D. The parameter is erased. The argument still points to the same object.
State of Memory
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25. Two-Dimensional Arrays
Intro to OOP with Java, C. Thomas Wu
Two-Dimensional Arrays
Two-dimensional arrays are useful in representing tabular information.
In Java, data may be organized in a two-dimensional array.
A table is an example of a two-dimensional array.
In a two-dimensional array, two indices (in a table, one for the row and one for the column) are used to refer to the array element.
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26. Declaring and Creating a 2-D Array
Intro to OOP with Java, C. Thomas Wu
Declaring and Creating a 2-D Array
Declaration
<data type> [][] <variable> //variation 1
<data type> <variable>[][] //variation 2
Creation
<variable> = new <data type> [ <size1> ][ <size2> ]
Example 3 2 1 4
payScaleTable
payScaleTable = new double[4][5];
is really a shorthand for
payScaleTable = new double[4][ ];
payScaleTable[0] = new double[5];
payScaleTable[1] = new double[5];
payScaleTable[2] = new double[5];
payScaleTable[3] = new double[5];
which is equivalent to
for (int i = 0; i < 4; i++) {
payScaleTable[i] = new double[5]; }
double[][] payScaleTable;
payScaleTable
= new double[4][5];
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27. Intro to OOP with Java, C. Thomas Wu
Accessing an Element
An element in a two-dimensional array is accessed by its row and column index.
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28. Sample 2-D Array Processing
Intro to OOP with Java, C. Thomas Wu
Sample 2-D Array Processing
Find the average of each row.
double[ ] average = { 0.0, 0.0, 0.0, 0.0 };
for (int i = 0; i < payScaleTable.length; i++) {
for (int j = 0; j < payScaleTable[i].length; j++) {
average[i] += payScaleTable[i][j]; }
average[i] = average[i] / payScaleTable[i].length;
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29. Java Implementation of 2-D Arrays
Intro to OOP with Java, C. Thomas Wu
Java Implementation of 2-D Arrays
The sample array creation
payScaleTable = new double[4][5];
is really a shorthand for
payScaleTable = new double [4][ ];
payScaleTable[0] = new double [5];
payScaleTable[1] = new double [5];
payScaleTable[2] = new double [5];
payScaleTable[3] = new double [5];
The concept of the two-dimensional array in Java is just that: a concept. There is no explicit structure called the “two-dimensional array” in Java.
The two-dimensional array concept is implemented by using an array of arrays.
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30. Two-Dimensional Arrays
Intro to OOP with Java, C. Thomas Wu
Two-Dimensional Arrays
Subarrays may be different lengths.
Executing
triangularArray = new double[4][ ];
for (int i = 0; i < 4; i++)
triangularArray[i] = new double [i + 1];
results in an array that looks like:
An array that is part of another array is called a subarray.
An array of arrays may be initialized when it is created.
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31. Intro to OOP with Java, C. Thomas Wu
Lists and Maps
The java.util standard package contains different types of classes for maintaining a collection of objects.
These classes are collectively referred to as the Java Collection Framework (JCF).
JCF includes classes that maintain collections of objects as sets, lists, or maps.
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32. Intro to OOP with Java, C. Thomas Wu
Java Interface
A Java interface defines only the behavior of objects
It includes only public methods with no method bodies.
It does not include any data members except public constants
No instances of a Java interface can be created
One Java interface we have seen is the ActionListener interface. The declaration for an interface includes the reserved word 'interface'. In the declaration, we list the method headers (i.e. a method without body) only.
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33. Intro to OOP with Java, C. Thomas Wu
JCF Lists
JCF includes the List interface that supports methods to maintain a collection of objects as a linear list
L = (l0, l1, l2, , lN)
We can add to, remove from, and retrieve objects in a given list.
A list does not have a set limit to the number of objects we can add to it.
A list being linear means the object, or elements, in the list are positioned in a linear sequence. That is, l0 is the first element, l1 is the second element, and so forth. A list has not size limit; there is no set limit to the number of elements we can add to a list.
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34. Intro to OOP with Java, C. Thomas Wu
List Methods
Here are five of the 25 list methods:
boolean add ( Object o )
Adds an object o to the list
void clear ( )
Clears this list, i.e., make the list empty
Object get ( int idx )
Returns the element at position idx
boolean remove ( int idx )
Removes the element at position idx
int size ( )
Returns the number of elements in the list
There are total of 25 methods defined in the List interface. The five listed here are the very frequently used subset of those 25 methods.
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35. Intro to OOP with Java, C. Thomas Wu
Using Lists
To use a list in a program, we must create an instance of a class that implements the List interface.
Two classes that implement the List interface:
ArrayList
LinkedList
The ArrayList class uses an array to manage data.
The LinkedList class uses a technique called linked-node representation.
Because both the ArrayList and LinkedList classes implement the same interface, we know that instances of ArrayList and LinkedList behave the same way, i.e., they support the same set of public methods defined in the List interface.
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36. Intro to OOP with Java, C. Thomas Wu
Sample List Usage
Here's an example of manipulating a list:
import java.util.*;
List friends;
Person person;
friends = new ArrayList( );
person = new Person("jane", 10, 'F');
friends.add( person );
person = new Person("jack", 6, 'M');
Person p = (Person) friends.get( 1 );
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37. Intro to OOP with Java, C. Thomas Wu
JCF Maps
JCF includes the Map interface that supports methods to maintain a collection of objects (key, value) pairs called map entries.
key
value k0 k1 kn v0 v1 vn .
one entry
We can add to, remove from, and retrieve objects in a given list.
A list does not have a set limit to the number of objects we can add to it.
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38. Intro to OOP with Java, C. Thomas Wu
Map Methods
Here are five of the 14 list methods:
void clear ( )
Clears this list, i.e., make the map empty
boolean containsKey ( Object key )
Returns true if the map contains an entry with a given key
Object put (Object key, Object value)
Adds the given (key, value) entry to the map
boolean remove ( Object key )
Removes the entry with the given key from the map
int size ( )
Returns the number of elements in the map
There are total of 14 methods defined in the List interface. The five listed here are the very frequently used subset of these 14 methods.
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39. Intro to OOP with Java, C. Thomas Wu
Using Maps
To use a map in a program, we must create an instance of a class that implements the Map interface.
Two classes that implement the Map interface:
HashMap
TreeMap
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40. Intro to OOP with Java, C. Thomas Wu
Sample Map Usage
Here's an example of manipulating a map:
import java.util.*;
Map catalog;
catalog = new TreeMap( );
catalog.put("CS101", "Intro Java Programming");
catalog.put("CS301", "Database Design");
catalog.put("CS413", "Software Design for Mobile Devices");
if (catalog.containsKey("CS101")) {
System.out.println("We teach Java this semester");
} else {
System.out.println("No Java courses this semester"); }
The (key, value) pair for this sample map is the course number and the course title, respectively.
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41. Intro to OOP with Java, C. Thomas Wu
Problem Statement
Write an AddressBook class that manages a collection of Person objects. An AddressBook object will allow the programmer to add, delete, or search for a Person object in the address book.
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42. Overall Plan / Design Document
Intro to OOP with Java, C. Thomas Wu
Overall Plan / Design Document
Since we are designing a single class, our task is to identify the public methods.
Public Method
Purpose
AddressBook
A constructor to initialize the object. We will include multiple constructors as necessary.
add
Adds a new Person object to the address book.
delete
Deletes a specified Person object from the address book.
search
Searches a specified Person object in the address book and returns this person if found.
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43. Intro to OOP with Java, C. Thomas Wu
Development Steps
We will develop this program in five steps:
Implement the constructor(s).
Implement the add method.
Implement the search method.
Implement the delete method.
Finalize the class.
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44. Intro to OOP with Java, C. Thomas Wu
Step 1 Design
Start the class definition with two constructors
The zero-argument constructor will create an array of default size
The one-argument constructor will create an array of the specified size
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45. Intro to OOP with Java, C. Thomas Wu
Step 1 Code
Directory: Chapter10/Step1
Source Files: AddressBook.java
Program source file is too big to list here. From now on, we ask
you to view the source files using your Java IDE.
Please use your Java IDE to view the source files and run the program.
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46. Intro to OOP with Java, C. Thomas Wu
Step 1 Test
The purpose of Step 1 testing is to verify that the constructors work as expected.
Argument to Constructor
Purpose
Negative numbers
Test the invalid data.
Test the end case of invalid data. 1
Test the end case of valid data.
>= 1
Test the normal cases.
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47. Intro to OOP with Java, C. Thomas Wu
Step 2 Design
Design and implement the add method
The array we use internal to the AddressBook class has a size limit, so we need consider the overflow situation
Alternative 1: Disallow adds when the capacity limit is reached
Alternative 2: Create a new array of bigger size
We will adopt Alternative 2
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48. Intro to OOP with Java, C. Thomas Wu
Step 2 Code
Directory: Chapter10/Step2
Source Files: AddressBook.java
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49. Intro to OOP with Java, C. Thomas Wu
Step 2 Test
The purpose of Step 2 test is to confirm that objects are added correctly and the creation of a bigger array takes place when an overflow situation occurs.
Test Sequence
Purpose
Create the array of size 4
Test that the array is created correctly.
Add four Person objects
Test that the Person objects are added correctly.
Add the fifth Person object
Test that the new array is created and the Person object is added correctly (to the new array).
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50. Intro to OOP with Java, C. Thomas Wu
Step 3 Design
Design and implement the search method.
loc = 0;
while ( loc < count &&
name of Person at entry[loc] is not equal to
the given search name ) {
loc++; }
if (loc == count) {
foundPerson = null;
} else {
foundPerson = entry[loc];
return foundPerson;
Here's the pseudocode to locate a person with the designated name. Notice that for this routine to work correctly, the array must be packed with the real pointers in the first half and null pointers in the last half.
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51. Intro to OOP with Java, C. Thomas Wu
Step 3 Code
Directory: Chapter10/Step3
Source Files: AddressBook.java
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52. Intro to OOP with Java, C. Thomas Wu
Step 3 Test
To test the correct operation of the search method, we need to carry out test routines much more elaborate than previous tests.
Test Sequence
Purpose
Create the array of size 5 and add five Person objects with unique names.
Test that the array is created and set up correctly. Here, we will test the case where the array is 100 percent filled.
Search for the person in the first position of the array
Test that the successful search works correctly for the end case.
Search for the person in the last position of the array
Test another version of the end case.
Search for a person somewhere in the middle of the array.
Test the normal case.
Search for a person not in the array.
Test for the unsuccessful search.
Repeat the above steps with an array of varying sizes, especially the array of size 1.
Test that the routine works correctly for arrays of different sizes.
Repeat the testing with the cases where the array is not fully filled, say, array length is 5 and the number of objects in the array is 0 or 3.
Test that the routine works correctly for other cases.
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53. Intro to OOP with Java, C. Thomas Wu
Step 4 Design
Design and implement the delete method.
boolean status;
int loc;
loc = findIndex( searchName );
if ( loc is not valid ) {
status = false;
} else { //found, pack the hole
replace the element at index loc+1 by the last element
at index count;
status = true;
count--; //decrement count, since we now have one less element
assert 'count' is valid; }
return status;
Here's the pseudocode to delete a person with the designated name. First we locate the person. If the person is not found, we exit the delete routine. If the person is found, then we remove it and fill the hole.
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54. Intro to OOP with Java, C. Thomas Wu
Step 4 Code
Directory: Chapter10/Step4
Source Files: AddressBook.java
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55. Intro to OOP with Java, C. Thomas Wu
Step 4 Test
To test the correct operation of the delete method, we need to carry out a detailed test routine.
Test Sequence
Purpose
Create the array of size 5 and add five Person objects with unique names.
Test the array is created and set up correctly. Here, we will test the case where the array is 100 percent filled.
Search for a person to be deleted next.
Verify that the person is in the array before deletion.
Delete the person in the array
Test that the delete method works correctly.
Search for the deleted person.
Test that the delete method works correctly by checking the value null is returned by the search.
Attempt to delete a nonexisting person.
Test that the unsuccessful operation works correctly.
Repeat the above steps by deleting persons at the first and last positions.
Test that the routine works correctly for arrays of different sizes.
Repeat testing where the array is not fully filled, say, an array length is 5 and the number of objects in the array is 0 or 3.
Test that the routine works correctly for other cases.
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56. Intro to OOP with Java, C. Thomas Wu
Step 5: Finalize
Final Test
Since the three operations of add, delete, and search are interrelated, it is critical to test these operations together. We try out various combinations of add, delete, and search operations.
Possible Extensions
One very useful extension is scanning. Scanning is an operation to visit all elements in the collection.
Scanning is useful in listing all Person objects in the address book.
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