This chapter discusses how to create external classes in Java, including defining constructors and instance methods. It covers how to declare and initialize arrays, use counter-controlled for loops with assignment and unary operators, and implement layout managers. The chapter also presents a reservations program example to demonstrate these concepts, with classes for managing rooms and handling window events.

1. Java Programming, 3e
Concepts and Techniques
Chapter 5
Arrays, Loops, and
Layout Managers Using
External Classes

2. 2Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Chapter Objectives
• Create and implement an external class
• Write code to create a constructor class
method
• Construct an instance method to initialize
instance variables
• Declare and construct an array using
correct notation

3. 3Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Chapter Objectives
• Use layout managers with container
components
• Code a counter-controlled loop using the
for statement
• Correctly employ assignment and unary
operators
• Use methods with Frame, Panel, TextArea
and Choice components

4. 4Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Introduction
• This chapter illustrates how to create an object,
complete with methods and attributes
• Objects have three key characteristics
– Identity
• The object can be called and used as a single unit
– State
• The object has various properties whose values might
change
– Behavior
• The object can perform actions and have actions performed
upon it

5. 5Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
The Reservations Program
• A stand-alone windowed application.

6. 6Chapter 5: Arrays, Loops, and Layout Managers Using External Classes

7. 7Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Problem Analysis
• When the user enters information and clicks the Book
Room button, some visual element should change in the
user interface to indicate the current status
• The program should be designed to easily accommodate
modifications in the number of party rooms

8. 8Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Design the Solution

9. 9Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Design the Solution
• TextArea components display larger
amounts of information than TextFields
• TextFields allow user entries
• A Choice component displays a drop-
down list, which ensures valid entries
• A hidden checkbox component is used to
clear the checkbox options
• A button triggers an event

10. 10Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Program Design
• The Reservations class is the driver class
• Create variable dictionaries
– A class list of variables with their type and purpose
• Create method prototypes, headers, and flowcharts

11. 11Chapter 5: Arrays, Loops, and Layout Managers Using External Classes

12. 12Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
• Methods in the Reservation class
• Constructor methods
– Define an instance of an object
– Have no return data type
– Have the same name as the object
– Create an instance of the object internally

13. 13Chapter 5: Arrays, Loops, and Layout Managers Using External Classes

14. 14Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Rooms Class

15. 15Chapter 5: Arrays, Loops, and Layout Managers Using External Classes

16. 16Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Creating an External Class
• An external class is a class that is not a driver class
• The Rooms class is an external class
• External classes are declared public to be accessible by
all objects and to allow for inheritance

17. 17Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Arrays
• An array stores multiple data items of the same
type in a single storage location
• Declare an array with the element type, a set of
square brackets, and the array identifier name
– int[] ages; or int ages[];
• Construct an array with the new keyword and
the array length, or number of elements
– ages = new int[100];
– int[] ages = new int[100];

18. 18Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Arrays
• Retrieve the array’s length using the length
property
– int size = arrayName.length
• Assign values and access array elements using
the index number of the element
– An index number is assigned to each element,
beginning at zero and progressing by integers
– temperature[3] = 78;
• Declare, construct, and assign values with one
statement
– boolean[] results = {true, false, true, false, true};

19. 19Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Arrays
• Index numbers can be any expression that
evaluates to an integer
• Array elements can be used anywhere a
variable is used
– overtime = (hours[6] - 40) * rate[6] * 1.5
• Two-dimensional arrays are used to create
tables of values
– Two index numbers represent the number of rows
and columns.
– int[][] myTable = new int[4,3];

20. 20Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Constructing an Instance
• Create a constructor method for the class
• Declare a class variable and call the class
constructor in the driver class
• A class may have multiple constructors, each
with different arguments
– The practice of defining multiple methods with the
same name is called method overloading.

21. 21Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Counter-Controlled Loops
• A counter-controlled loop executes a specific
number of times
• Java uses a for loop to implement a counter-
controlled loop
• Assignment and unary operators are often used
to update the counter
– An assignment operator performs an arithmetic and
assignment operation all with one operator, thus
providing a shortcut
– A unary operator only needs one operand to perform
its function

22. 22Chapter 5: Arrays, Loops, and Layout Managers Using External Classes

23. 23Chapter 5: Arrays, Loops, and Layout Managers Using External Classes

24. 24Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Unary operators behave differently depending on whether
the operator is positioned before or after the variable

25. 25Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Unary Operators in for Loops
• A for loop often uses the increment operator to
access each element of an array
• To exit a for loop prematurely, assign the
counter a number outside the condition range
inside the loop

26. 26Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Instance Methods
• An instance method operates or manipulates
variables for an external class
• Instance variables are variables manipulated
within an instance method, which are local in
scope
• When called by a driver class, instance methods
must use the class.method() notation
• Instance methods typically include a user-
friendly active verb in the method name

27. 27Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
The bookRoom() Method

28. 28Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Creating Windowed Applications
• The AWT classes are abstract and provide only
essential components which are obtained from
the native environment when instantiated
• The Swing components use lightweight Java
implementations of standard GUI controls
• A container is an object that contains other
components
– A Frame is a container for a collection of graphical
AWT components.
– A program using a Frame needs to use the word,
extends, in the class header.

29. 29Chapter 5: Arrays, Loops, and Layout Managers Using External Classes

30. 30Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
The Reservations Class

31. 31Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Choice Components
• A Choice component displays a restricted list through a
drop-down list box with a box arrow

32. 32Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Calling Constructor Methods for
the Reservations Class

33. 33Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Layout Managers
• Layout managers assist programmers organize
components into predefined locations in a window
• If the user resizes the window, the size and position of
the components are automatically adjusted

34. 34Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Flow Layout
• Change alignment with setLayout() and the constructor
• Add components with the add() method

35. 35Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
BorderLayout
• The add() method takes a parameter specifying the
desired region
• The setLayout() method takes two integers parameters
to specify the number of pixels between components

36. 36Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
GridLayout
• All components must be the same size
• The constructor takes the number of rows and columns
as parameters

37. 37Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
CardLayout
• Each card may have its own layout manager
• Only the top card on the stack is visible

38. 38Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
GridBagLayout
• Components can be of varying size and can be added in
any order

39. 39Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
The Reservations() Constructor

40. 40Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Window Event-Handling
Methods
• A WindowListener is registered with a Frame with the
addWindowListener() method
• A WindowAdapter class is used to provide the event-
handling methods for the Frame
– Adapter classes implement abstract classes, providing
prewritten method for all the methods, any of which can be
overridden by the programmer

41. 41Chapter 5: Arrays, Loops, and Layout Managers Using External Classes

42. 42Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
The main() Method
• Execution of a program begins with the
main() method
• The main() method can be placed
anywhere within the class braces
• In a windowed application, the main()
method creates the instance of the Frame
using a call to the constructor method
• The main() method also sets attributes for
the Frame

43. 43Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
The main() Method

44. 44Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
The actionPerformed() Method

45. 45Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
The clearFields() Method
• Clears input fields after a successful booking.

46. 46Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Testing a Windowed Application
• Compile and correct errors
• Use multiple test cases to test maximum values
• Test with incorrect data

47. 47Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Chapter Summary
• Create and implement an external class
• Write code to create a constructor class
method
• Construct an instance method to initialize
instance variables
• Declare and construct an array using
correct notation

48. 48Chapter 5: Arrays, Loops, and Layout Managers Using External Classes
Chapter Summary
• Use layout managers with container
components
• Code a counter-controlled loop using the
for statement
• Correctly employ assignment and unary
operators
• Use methods with Frame, Panel, TextArea
and Choice components

49. Java Programming, 3e
Concepts and Techniques
Chapter 5 Complete
Arrays, Loops, and
Layout Managers Using
External Classes