1 INVALID & VALID PARTY & FAVOR CHOICES P.docx

1
***INVALID & VALID PARTY & FAVOR CHOICES***
Party Themes
1. Anniversary
2. Birthday
3. Graduation
Enter your theme: 4
Invalid theme! Try again.
Party Themes
1. Anniversary
2. Birthday
3. Graduation
Enter your theme: 1
How many people will be invited to your Anniversary party? 10
Make your party favor selections. The cost is per guest.
1. Party Favors for Women $3.00
2. Party Favors for Men $3.00
3. Party Favors for Kids $2.00
4. Party Favors for Teenages $3.00

5. Exit
Enter your choice: 1
How many of your guests are women? 4
Do you want to make another party favor selection?
Enter Y or N: Y
5. Exit
How many of your guests are men? 5
Enter Y or N: N
The number of favors you bought doesn't equal the number of
guests.
Run through the selection of the favors again.

2
5. Exit
How many of your guests are women? 5
Enter Y or N: y
5. Exit
How many of your guests are men? 5
Enter Y or N: n
Party: Anniversary
Cost: $150.00
IS 2031: LE 5.3 - Methods Student
Name:

1. Write the following static methods. Assume the reference
variable input for the Scanner class and any global variables
mentioned are already declared. All other variables will have to
be declared as local unless they are parameter variables. Use
printf.
a. A method that prompts for the party theme and returns the
theme. Print the message “Invalid theme! Try again.” if the
theme is out of range. Re-prompt until a valid entry is made.
Prompt: Party Themes
1. Anniversary
2. Birthday
3. Graduation
Enter your theme:
b. A value-receiving method that accepts the theme, and asks
for the number of guests and returns that number.
Prompt: How many people will be invited to your
xxxxxxxxxxxx party? where the Xs is the name of the theme
from 1a. The variable storing the name of the theme is global.

c. A value-receiving method that accepts the number of guests
and returns the cost for the food. Assume the cost per guest is
$12.00.
d.
A method that accepts the number of guests, prompts for party
favors and returns the cost. Allow for multiple party favors to
be chosen.
Prompt: Make your party favor selections. The cost is per
guest.
4. Party Favors for Teenagers $3.00
5. Exit
Enter your choice:
e. A method that accepts the cost for the food and the party
favors and calculates the total cost for the party and prints it:
(
where
the Xs is the
party theme
and the Zs is the total cost.

)
Party: Xxxxxxxxxxxxxxx
Cost: $Z,ZZ9.99
2. Write statements that will call each of the methods you
coded above. Store the values returned by the value-returning
methods in variables local to the main() where main() is in the
same class.
a.
b.
c.
d.
e.
1
Chapter 5, Methods
Java How to Program,
Late Objects Version, 10/e
© 1992-2015 by Pearson Education, Inc. All Rights Reserved.

5-2
5.1 Introduction to Methods
5.2 Calling Methods
5.3 Class Members
Instance Members
static Members
5.4 Value-Returning & Value-Receiving
Methods
5.5 Notes on Declaring & Using Methods
5.7 Passing Arguments to a Method
5.11 Scope of Variable Declarations
5.12 Method Overloading
Source: Gaddis, Tony, Starting Out with Java From Control
Structures through Objects 4th Edition, Pearson Education Inc.,
2010, Chapter 5.
Chapter 5 Topics
2

5-3
5.1 Why Write Methods?
Divide and Conquer: Methods break a problem down into small
manageable pieces.
A method
1contains code that performs a specific task.
2simplifies programs because a method can be used in several
places in a program. This is known as code reuse (method
coded once, used many times).
facilitates the design, implementation, operation and
maintenance of large programs.
Programs can be created from standardized methods rather than
by building customized code.
Dividing a program into meaningful methods makes the program
easier to debug and maintain.
2010, Chapter 5.
Source: 1Linda Shepherd, Dept. of ISCS, COB, UTSA.
Modified By: 2Linda Shepherd, Dept. of ISCS, COB, UTSA.
3
5-4
A method can have its own variables (local variables).

These variables are declared in the body of the method and
belongs only to that method.
Declaration Format:
dataType variableName = initializationValue;
A method also can use fields (class/global variables).
Fields can be used by more than one method.
Fields have to be static if the methods calling them are static.
Fields are to be declared as private.
Fields are declared at the beginning of a class.
Declaration Format:
private static dataType variableName = initializationValue;
©Linda Shepherd, Dept. of ISCS, COB, UTSA.
5.1 Methods & Variables
4
5-5
5.1 Method Declaration & Header
2010, Chapter 5.
public static void displayMessage()
{
System.out.printf(“%nHello“);

}
Body
Header
public static void displayMessage ()
{
System.out.printf(“%nHello“);
}//This method receives nothing and returns
//nothing.
Method Modifiers
Return Type
Method Name
Parameter List
empty,

i.e., no para-
meter variables
5
1A return allows a method to pass or give back a value.
Therefore, it has to be typed for the value it’s returning. The
return type can be void, a primitive data type (int, char, byte,
short, long, float, double, boolean), or complex data type
(classes such as String or any other class). ©Linda Shepherd,
Dept. ISTM, COB, UTSA
5-6
5.1 Parts of a Method Header
public static String getName ()
{
Scanner input = new Scanner(System.in);
System.out.printf(“%nWhat is your name? “);
String name = input.nextLine();
return name;
}//This is a value-returning method.
Method Modifiers

1Return Type
Method Name
Parameter List
2010, Chapter 5.
6
1Parameter variables are variables listed within the parentheses
or parameter list. They can be of any data type - primitive data
type (int, char, byte, short, long, float, double, boolean), or
complex data type (classes such as String or any other class).
They are local to the method and help the method receive data
for processing. The paramater variable name is an object of the
String class. ©Linda Shepherd, Dept. ISTM, COB, UTSA
5-7
public static void printName (String name)
{
System.out.printf(“Your name is %s.”, name);
}//This is a value-receiving method.

Method Modifiers
Return Type
Method Name
Parameter List
2010, Chapter 5.
with 1 parameter variable
7
5-8
2010, Chapter 5.
public static int sum(int num1, int num2)
{
int result = 0;

result = num1 + num2;
return result;
}//This is a value-returning & value-receiving
//method.
Method Modifiers
Method Name
Parentheses
Return Type
contain a parameter list
8
5-9
1A void method is one that simply performs a task and then
terminates.

System.out.printf(“%nHi!");
2It can receive or not receive data.
3It definitely doesn’t return data.
4It has to be static if it’s in the same class as another static
method that calls it.
Source: 1Gaddis, Tony, Starting Out with Java From Control
2010, Chapter 5.
2,3,4Linda Shepherd, Dept. of ISCS, COB, UTSA.
5.1 static and void Methods
9
5-10
public class DemoStaticVoidMethod
{
private static String personName;
private static Scanner input = new
Scanner (System.in);
public static void main(String[] args)
{
String greeting = “Hello”;
setName();
System.out.printf(“%s %s!”, greeting, personName);
System.exit(0);

}//END main()
public static void setName()
{
System.out.print(“Enter your name: “);
personName = input.nextLine();
}//END setName()
}//END APPLICATION CLASS DemoStaticVoidMethod
10
5-11
A value-returning method not only performs a task, but also
sends a value back to the code that called it.
name = input.nextLine();
System.out.printf(“Hi %s!”, name); OR
System.out.printf(“Hi %s!”, getName());
2010, Chapter 5.
Method that returns a name
see slides 5-6

5.1 Value-Returning Methods
nextLine is a method that captures a name and returns it to be
stored in the variable name; therefore,
nextLine is a value-returning method.
11
5-12
A value-receiving method not only performs a task, but also
gets a value or values from the code that calls it.
System.out.println(“Hi “ + name + “!” );
OR
System.out.printf(“Hi %s!”, getName());
2010, Chapter 5.
5.1 Value-Receiving Methods
“Hi “ plus the value in name plus “!” are all concatenated
(joined) then sent to println which is a value-receiving method
This String value/literal containing a name is sent to printf()
which in turn displays the greeting; therefore, printf is a value-
receiving method, but printf is also value-returning because it
returns the formatted output which is then printed.

12
5-13
Methods are real important because they are how programs can
share code and interact one another. One method (the client)
from one class can call the method of another class to use that
method’s code (or services).
The method header has
Modifiers usually: public static
A return type: void, primitive or complex data type
Method name: should describe the method’s purpose
Parentheses: the parameter list that can be empty or contain a
list of parameter variables with their data types.
void methods return nothing.
Value-returning methods have a return type other than void.
They return or give back data to the code that calls it. The data
has to have the same data type as the return type.
They must have only one return statement as the last statement
in the method body.
5.1 Methods: Summary

13
5-14
A method with empty parentheses or no variables in its
parameter list receives nothing – no data – from the code that
calls it.
Value-receiving methods accept or receive data from the code
that calls it.
The type of data and how much data sent to a method is dictated
by its parameter list (what is inside the parentheses).
Data sent has to be in the same order as what is listed in the
parameter list.
Methods that are in the same program and are static can only
interact with other static methods and can only use global
variables (fields) that are static.
static means that there is only one of that method or variable in
existence during runtime.
Variables that are global are declared at the class level right
after the open brace { for the class.
They should be declared private.
5.1 Methods: Summary (cont)

14
5-15
Methods are written so code can be grouped according to its
purpose or function.
This allows for code to be reused without having to be re-
written.
This makes debugging easier.
This allows the programmer to call the method with the code
that is needed when and where it’s needed.
Program maintenance is easier because any changes to a
program can be targeted to the method that needs changing, so
the other parts of the program remain unaffected.
5.1 Methods: Summary (cont)
15
A method has to be called or invoked to use its code. Methods
coded in the same program are called directly using its name.
displayMessage();
1Methods coded in another program (class) … are called by …
objects:

Where input is an object of the Scanner class.
2Methods coded in another class that are static … can be called
using the class name …
int highValue = Math.max(8,5);
Never call methods with the header intact:
public static void displayMessage();
5.2 Calling Methods
5-16
Modified By: 1,2Linda Shepherd, Dept. of ISCS, COB, UTSA.
5-17
Methods in the same class are called/invoked using their name
followed by parentheses.
methodName();
Methods from other classes that are static can be called using
the name of the class followed by a dot operator and the method
name and parentheses.
ClassName.methodName();
Methods from other classes can be called using an object of the
class. These methods are usually non-static.
objectName.methodName();
5.2 Calling Methods: Summary

17
5-18
5.3 static Class Members
The fields and methods of a class are referred to as class
members. Class members can be static or non-static (also
known as instance members).
Within the same class, static methods can only
access static fields,
call other static methods.
To invoke (call) a public static method or use a public static
field from another class, the class name, rather than the instance
name, is used.
Example: double val = Math.sqrt(25.0);
2010, Chapter 9.
1, 2©Linda Shepherd, Dept. of ISCS, COB, UTSA.
Class name
Static method

18
5-19
Methods can … be declared static by placing the keyword static
between the access modifier and the return type of the method.
public static double milesToKilometers(double miles)
{…}
When a class contains a static method, it is not necessary to
create an instance (copy) of the class in order to use the method.
double kilosPerMile = Metric.milesToKilometers(1.0);
Examples: Metric.java, MetricDemo.java
2010, Chapter 9.
5.3 static Methods
19

5-20
static methods are convenient because they may be called at the
class level, i.e., using the class name.
They are typically used to create utility classes, such as the
Math class in the Java Standard Library (Java API).
2010, Chapter 9.
5.3 static Methods
20
5-21
{
private static Scanner input = new
Scanner (System.in);
public static String setName()
{
return input.nextLine();
}//END setName()
}//END CLASS DemoStaticVoidMethod
public class TestDemoStaticVoidMethod

{
{ String greeting = “Hello”;
System.out.printf(“%s %s!”, greeting,
DemoStaticVoidMethod.setName());
System.exit(0);
}//END main()
}//END APPLICATION CLASS TestDemoStaticVoidMethod
//NO IMPORT STMT NEEDED IN Test IF BOTH CLASSES IN
SAME DIRECTORY
21
5-22
{
private static Scanner input = new Scanner (System.in);
public static String setName()
{
return input.nextLine();
}//END setName()
}//END CLASS DemoStaticVoidMethod
public class TestDemoStaticVoidMethod
{

{ DemoStaticVoidMethod demoProg =
new DemoStaticVoidMethod();
String greeting = “Hello”;
System.out.printf(“%s %s!”, greeting,
demoProg.setName());
System.exit(0);
}//END main()
}//END APPLICATION CLASS TestDemoStaticVoidMethod
//NO IMPORT STMT NEEDED IN Test IF BOTH CLASSES IN
SAME DIRECTORY
demoProg is an object of DemoStaticVoidMethod class.
22
5-23
There are 2 types of class members:
Global variables or fields
Methods
These members can be static or non-static.
static members are coded with the word static whereas non-
static members aren’t.
In the same program, static methods can only
interact with other static methods.
use static fields.

Note: The variables coded in a method are not fields. They are
local or method level variables and they are never static.
Therefore programs with the main() will be coded with static
methods and static fields because the main() is static.
5.3 static Members: Summary
23
5-24
A method can only return a single value to a calling statement
through its return-type.
public static String yourName()
A method can receive values through its parameter list.
public static void yourName(String first, String last)
A method can receive one or more values and return a value.
public static String yourName(String first, String last)
5.4 Value-Returning and Value-Receiving Methods
©Linda Shepherd, Dept. of ISCS, COB, UTSA

24
5-25
{
int result = 0;
return result;
}
This [variable] must be of the same data type as the return type
Return type
The return statement causes the method to end execution and it
returns a value back to the statement that called the method.
2010, Chapter 5.
5.4 Defining a Value-Returning and Value-Receiving Method

25
5-26
{
int result = 0;
return result;
}
1Parameter List
contains a list of variables the method takes in for processing.
Parameter variables are local.
5.4 Defining a Value-Returning and Value-Receiving Method
2010, Chapter 5.
1Linda Shepherd, Dept. of ISCS, COB, UTSA.
26

5-27
5.4 Returning a Value from a Method
Data can be passed into a method by way of the parameter
variables. Data may also be returned from a method, back to
the statement that called it.
int num = Integer.parseInt("700");
The String literal “700” is passed to the parseInt method.
The int value 700 is returned from the method and assigned to
the num variable.
2010, Chapter 5.
27
5-28
total = sum(value1, value2);
}
{
int result = 0;
return result;

}
20
40
60
2010, Chapter 5.
5.4 Calling a Value-Returning and Value-Receiving Method
{
int value1 = 20;
int value2 = 40;
int total = 0;
These are variable arguments.
28

5-29
Sometimes we need to write methods to test arguments for
validity and return true or false
public static boolean isValid( int number )
{
boolean status = false;
if(number >= 1 && number <= 100)
{
status = true;
}
return status;
}
Calling code:
int value = 20;
if(isValid(value))
System.out.printf(“%nThe value is within range.“);
else
System.out.printf(“%nThe value is out of range.“);
5.4 Returning a boolean Value
2010, Chapter 5.
29

5-30
5.4 Returning a Reference to a String Object
customerName = fullName("John“, "Martin“);
public static String fullName(String first, String last)
{
String name = null;
name = first + " " + last;
return name;
}
See example:
ReturnString.java
Local variable name holds the reference to the object. The
return statement sends a copy of the reference back to the call
statement and it is stored in customerName.
address
“John Martin”
2010, Chapter 5.
These are literal arguments.

30
5-33
A method can be value-receiving only.
A method can be value-returning only.
A method can be both value-receiving and value-returning.

A method can be void and value-receiving.
A method can be void and NOT value-receiving or
parameterless (empty parentheses).
A method can be value-returning and NOT value-receiving.
A call to a value-returning method requires the calling
statement to handle that value by
Storing it in a variable of the same type which requires the use
of an assignment operator.
Printing it
Using it in some type of expression
Processing it in some way.
5.4 Value-Receiving & Value-Returning Methods: Summary
33
5-34
A call to a value-receiving method requires the calling
statement to send it data that matches the data type of the
parameter variables in the method’s parameter list.
The data sent has to be sent in the same order as what is listed
in the parameter list.
There is no limit to the number of parameter variables, but
practicality dictates that you make the method as simple as
possible.

The data sent to the method are called arguments.
There are variable arguments.
calc(num1, num2); where num1 and num2 are variables so
they’re being used as variable arguments.
There are literal arguments.
calc(10, 5); where 10 and 5 are integer literals so
they’re being used as literal arguments.
There are value-returning method arguments.
calc(val1(), val2()); where val1() and val2() are methods that
return the numbers sent to the calc method, so they’re used as
method arguments.
.
5.4 Value-Receiving & Value-Returning Methods: Summary
(cont)
34
5-35
What is sent to a method is an argument.
System.out.printf(“%nHello”);
number = Integer.parseInt(str);
The data type of an argument in a method call must correspond
to the 1data type of the parameter variable in the parentheses of

the method 2header. The parameter is the variable that holds the
value being passed to a method.
By using parameter variables in your method declarations, you
can design your own methods that accept data. See example:
PassArg.java
2010, Chapter 5.
1,2Linda Shepherd, Dept. of ISCS, COB, UTSA
5.7 Passing Arguments to a Value-Receiving Method
35
5-36
5.7 Passing 5 to the displayValue Method
displayValue(5);
public static void displayValue(int num)
{
System.out.printf(“The value is %d.“, num);
}
The argument 5 is an integer literal that is copied to the
parameter variable num.

The method will display The value is 5.
2010, Chapter 5.
36
5-37
5.7 Argument and Parameter Data Type Compatibility
When you pass an argument to a method, be sure that the
argument’s data type is compatible with the parameter
variable’s data type.
Java will automatically perform widening conversions, but
narrowing conversions will cause a compiler error.
double d = 1.0;
displayValue(d);
Error! Can’t convert double to int
2010, Chapter 5.

37
5-38
5.7 Passing Multiple Arguments
showSum(5, 10);
public static void showSum(double num1, double num2)
{
double sum = 0; //to hold the sum
sum = num1 + num2;
System.out.printf(“%nThe sum is %.0f“, sum);
}
The argument 5 is copied to the num1 parameter.
The argument 10 is copied to the num2 parameter.
NOTE: Order matters!
method call
2010, Chapter 5.

38
5-39
5.7 Arguments Passed by Value or by Reference
Passed by Value: In Java, all arguments of the primitive data
types are passed by value, which means that a copy of an
argument’s value is passed to a parameter variable.
If a parameter variable is changed inside a method, it has no
affect on the original argument.
See example: PassByValue.java
Passed by Reference: In Java, objects are passed by reference
which means the address (memory location) of the object is
passed/sent to a parameter variable.
Can the original object be affected if it’s changed inside the
method?
A method’s parameter variables are separate and distinct from
the arguments that are listed inside the parentheses of a method
call.
2010, Chapter 5.

39
5-40
Arguments passed to a value-receiving method must be of the
same type as the parameter variables.
Arguments of primitive data types are passed by value –
meaning a copy of the arguments are sent and stored in the
parameter variables so the method can use them.
Arguments of complex data types are passed by reference –
meaning an address of the object is sent and stored in the
parameter variable.
Parameter variables are local variables. They belong to the
method only.
Arguments must be sent in the order of the parameter variables;
otherwise, the data stored in the parameter variables are not
accurate.
There will be a compilation error if there is not the right
number or the right type of arguments sent.
5.7 Passing Method Arguments: Summary

40
5-41
A local variable is declared inside a method and is not
accessible to statements outside the method.
Different methods can have local variables with the same names
because the methods cannot see each other’s local variables.
A method’s local variables exist only while the method is
executing. When the method ends, the local variables and
parameter variables are destroyed and any values stored are
lost.
Local variables are not automatically initialized with a default
value and must be given a value before they can be used.
2010, Chapter 5.
5.11 Scope of Variable Declarations Local Variables
41
5-42
A class variable or class field is declared at the class level right
after the class header, following the open brace for the class.
It is accessible to all statements (methods) within the class and
is known as a global variable.
It is declared using access specifiers

private – which means only the statements inside the class can
use the field and is primarily used when declaring class fields
Useful in promoting data hiding
Protects variables from corruption or malicious alteration
public – which means statements inside or outside the class can
use the field
protected – which means statements in the same family of
classes can use the field
Class variables are automatically initialized when declared.
E.g.: private int age; //where age will be initialized to 0.
©Linda Shepherd, Dept. of ISCS, COB, UTSA
5.11 Scope of Variable Declarations Global Variables
42
5.11 Scope of Declarations
Any block may contain variable declarations
If a local variable or parameter in a method has the same name
as a field of the class, the class field is “hidden” until the block
terminates execution
Called shadowing
The application in Fig. 5.9 demonstrates scoping issues with
fields and local variables
5-43

5-45
5-46
Variables declared at the class level are global variables or

fields.
They are scoped to the class.
All the code within the class can use these variables.
Should be always declared as private unless told otherwise.
Variables declared at the method level are local variables.
They are scoped to the method only.
No other code in the same class can access a method’s
variables.
Class level and method level variables can have the same name,
but the method level variables take precedence.
To access the class level variable in the same method use the
name of the class followed by a dot operator and the field name.
5.11 Variable Scope: Summary
46
6-47
5.12 Overloading Methods
Two or more methods in a class may have the same name as
long as their parameter lists are different.
When this occurs, it is called method overloading.
Method overloading is important because sometimes you need
several different ways to perform the same operation.

2010, Chapter 6.
47
6-48
5.12 Overloaded Method add
public static int add(int num1, int num2)
{
return num1 + num2;
}
public static double add(double num1, double num2)
{
double sum = 0.0;
sum = num1 + num2;
return sum;
}
2010, Chapter 6.

48
6-49
5.12 Method Signature and Binding
A method signature consists of the method’s name and the data
types of the method’s parameters, in the order that they appear.
The return type is not part of the signature.
add(int, int)
add(double, double)
The process of matching a method call with the correct method
is known as static binding. The compiler uses the method
signature to determine which version of the overloaded method
to bind the call to.
Signatures of the add methods from previous slide
2010, Chapter 6.
49

5-52
5.12 Method Overloading Error

5-53
Methods in a program that have the same name are called
overloaded methods.
For the computer to know which method to call or bind to, the
method signature has to be different.
The signature is the method name along with the data types of
the parameter variables in the order listed.
Overloaded methods are helpful when you need to have a
method handle or process different types of data.
5.12 Method Overloading: Summary
53
5-54
A method should always be documented by writing comments
that appear just before the method header.
The comments should provide a brief explanation of the
method’s purpose.
The documentation comments begin with /** and end with */.
@return and @param tags can be used to describe a method’s

return value and/or parameter variables.
2010, Chapter 5.
54
/**
The sum method returns the sum of its two parameters.
@param num1 The first number to be added.
@param num2 The second number to be added.
@return The sum of num1 and num2.
*/
5-55
You can provide a description of the return value in your
documentation comments by using the @return tag.
General format
@return Description
See example: ValueReturn.java
The @return tag in a method’s documentation comment must
appear after the general description. The description can span
several lines.

2010, Chapter 5.
55
5-56
You can provide a description of each parameter in your
documentation comments by using the @param tag.
General format
@param parameterName Description
See example: TwoArgs2.java
All @param tags in a method’s documentation comment must
appear after the general description.The description can span
several lines.
2010, Chapter 5.
/**
The sum method returns the sum of its two parameters.
@param num1 The first number to be added.
@param num2 The second number to be added.
@return The sum of num1 and num2.
*/

1 INVALID & VALID PARTY & FAVOR CHOICES P.docx

Recommended

Recommended

More Related Content

Similar to 1 INVALID & VALID PARTY & FAVOR CHOICES P.docx

Similar to 1 INVALID & VALID PARTY & FAVOR CHOICES P.docx (20)

More from mercysuttle

More from mercysuttle (20)

Recently uploaded

Recently uploaded (20)

1 INVALID & VALID PARTY & FAVOR CHOICES P.docx