? 2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 1
Chapter 4
Defining Instantiable Classes
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 2
Chapter 4 Objectives
After you have read and studied this chapter,you
should be able to
Define an instantiable class with multiple methods and a
constructor.
Differentiate the local and instance variables.
Define and use value-returning methods.
Distinguish private and public methods.
Distinguish private and public data members.
Describe how the arguments are passed to the
parameters in method definitions.
Use System.out for temporary output to verify the
program code.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 3
Building Large Programs
Learning how to define instantiable classes is the first step
toward mastering the skills necessary in building large programs,
A class is instantiable if we can create instances of the class,
The MainWindow,InputBox,and OutputBox classes are all
instantiable classes while the Math class is not,
In this chapter you will learn how to define instantiable classes
and different types of methods included in the instantiable
classes.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 4
CurrencyConverter
Let’s start with an example to cover the basics of
defining instantiable classes.
In designing an instantiable class,we start with its
specification,namely,how we want the class and its
instances behave.
A CurrencyConverter object will perform a conversion
from a foreign currency and the U.S,dollar.
What would be the most natural way for us to
interact with CurrencyConverter objects?
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 5
fromDollar and toDollar Methods
We would like to have (at least) two methods for
conversion,fromDollar and toDollar.
CurrencyConverter yenConverter;
yenConverter = new CurrencyConverter();
double amountInYen
= yenConverter.fromDollar( 500);
double amountInUS
= yenConverter.toDollar(15000);
Converting
$500 US to yen.
Converting
15,000 yen to
US dollar.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 6
setExchangeRate Methods
Since the exchange rate fluctuates,we need a
method to set the exchange rate.
CurrencyConverter yenConverter;
yenConverter = new CurrencyConverter;
yenConverter.setExchangeRate( 106.55);
$1.00 US = 106.55 yen
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 7
Using Multiple Instances
Once the CurrencyConverter class is defined,we can
use its multiple instances.
CurrencyConverter yenConverter,markConverter;
double amountInYen,amountInMark,amountInDollar;
yenConverter = new CurrencyConverter();
yenConverter.setExchangeRate(130.77);
markConverter = new CurrencyConverter( );
markConverter.setExchangeRate(1.792);
amountInYen = yenConverter.fromDollar( 200 );
amountInMark = markConverter.fromDollar( 200 );
amountInDollar = yenConverter.toDollar( 10000 );
amountInMark = markConverter.fromDollar(amountInDollar);
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 8
Template for Class Definition
class
{
}
.,,
Import Statement
Class Comment
Describe the class in
the javadoc format.
Class Name
Declarations
Declare data members
shared by multiple
methods here.
Methods
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 9
The CurrencyConverter Class
/**
* This class is used to do the currency conversion
* between a foreign currency and the U.S,dollar.
*
* @author Dr,Caffeine
*/
class CurrencyConverter
{
/**
* how much $1.00 U.S,is worth in the foreign currency
*/
private double exchangeRate;
//method declarations come here
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 10
Method Declaration
<modifier> <return type> <method name> ( <parameters> )
{
<statements>
}
public void setExchangeRagte ( double rate )
{
exchangeRate = rate;
}
Statements
Modifier Return Type Method Name Parameter
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 11
Value-Returning Method
We call a method that returns a value a value-
returning method,or non-void method.
A value-returning method must include a return
statement in the following format:
return <expression> ;
public double toDollar( double foreignMoney )
{
return (foreignMoney / exchangeRate);
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 12
Method Header Comment in javadoc
/**
* Converts a given amount in dollars into
* an equivalent amount in a foreign currency.
*
* @param dollar the amount in dollars to be converted
*
* @return amount in foreign currency
*/
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 13
Constructors
A constructor is a special method that is executed
when a new instance of the class is created.
The purpose of the constructor is to initialize an
object to a valid state,Whenever an object is created,
we must ensure that it is created in a valid state by
properly initializing all data members in a constructor.
The name of a constructor must be the same as the
name of the class.
If no constructor is defined for a class (e.g.,the
original CurrencyConverter class),then the Java compiler will include a default constructor,
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 14
Default Constructor
The default constructor will have the following form,
public <class name> ( ){
}
public CurrencyConverter( )
{
}
A default constructor has
no statements in its
method body.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 15
Defining Constructors
A constructor will have the following form,
public <class name> ( <parameters ){
<statements>
}
public CurrencyConverter( double rate )
{
exchangeRate = rate;
}
This constructor
ensures that the value
for exchangeRate is
set when a new
instance is created.
Statements
Modifier Class Name Parameter
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 16
Multiple Constructors
A class can include multiple constructors without any
problem,as long as the constructors defined for the
class have either
A different number of parameters
Different data types for the parameters if the
number of parameters is the same
public MyClass( int value ) { … }
public MyClass( ) { … }
public MyClass( float value ) { … }
These constructors will
not conflict with each
other,and therefore,valid.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 17
Visibility Modifiers,public and private
The modifiers public and private designate the
accessibility of data members and methods.
If a class component (data member or method) is
declared private,no outside methods can access it.
If a class component is declared public,any outside
method can access it.
class Test
{
public int memberOne;
private int memberTwo;
}
Test myTest = new MyTest();
myTest.memberOne = 10;
myTest.memberTwo = 20;
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 18
Data Members Should Be private
Declare the data members (class and instance
variables) private to ensure the integrity of the class.
Data members are the implementation details of the
class,and they should be kept invisible from the
outside by declaring them private.
If a data member is declared public,then we cannot
make changes to the data member without affecting
all the classes that made direct access to this data member.
Constants can (should) be declared public if they are meant to be used directly by the outside methods.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 19
Local Variables
We covered instance and class variables that are
shared among the methods of the class.
A local variable is a variable that is declared within a
method declaration.
Local variables are accessible only from the method
in which they are declared.
Memory space for local variables are allocated only
during the execution of the method,When the
method execution completes,memory space will be
deallocated.
The parameters of a method are local to the method.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 20
Sample Method
public double fromDollar( double dollar )
{
double amount,fee;
fee = exchangeRate - feeRate;
amount = dollar * fee;
return amount;
}
Parameter
Local
Variables
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 21
Memory Allocation for Local Variables - 1
Code
State of
Memory
amt
= yenConverter.fromDollar( 200 );
public double fromDollar( double
dollar )
{
double amount,fee;
fee = exchangeRate - feeRate;
amount = dollar * fee;
return amount;
}
A
A,Local variables do
not exist before the
method execution
At before fromDollarA
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 22
Memory Allocation for Local Variables - 2
Code
amt
= yenConverter.fromDollar( 200 );
public double fromDollar( double
dollar )
{
double amount,fee;
fee = exchangeRate - feeRate;
amount = dollar * fee;
return amount;
}
B
State of
Memory
B,Memory space is
allocated for the local
variables and parameter.
After is executedB
dollar
amount
200.0
fee
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 23
Memory Allocation for Local Variables - 3
Code
amt
= yenConverter.fromDollar( 200 );
public double fromDollar( double
dollar )
{
double amount,fee;
fee = exchangeRate - feeRate;
amount = dollar * fee;
return amount;
}
C
State of
Memory
C,Computed values
are assigned to the local
variables.
After is executedC
dollar
amount
200.0
fee
24846.3
124.2315
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 24
Memory Allocation for Local Variables - 4
Code
amt
= yenConverter.fromDollar( 200 );
public double fromDollar( double
dollar )
{
double amount,fee;
fee = exchangeRate - feeRate;
amount = dollar * fee;
return amount;
}
D
State of
Memory
D,Memory space is
deallocated upon exiting
the fromDollar method.
At after fromDollarD
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 25
Pass-By-Value Scheme - 1
State of
Memory
public void myMethod( int one,float
two )
{
one = 25;
two = 35.4f;
}
A
A,Local variables do
not exist before the
method execution
At before myMethodA
Code
x = 10;
y = 20;
tester.myMethod( x,y );
x 10
y 1020
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 26
Pass-By-Value Scheme - 2
State of
Memory
B,The values of
arguments are copied
to the parameters.
Values are copied at B
public void myMethod( int one,float
two )
{
one = 25;
two = 35.4f;
}
Code
x = 10;
y = 20;
tester.myMethod( x,y ); B
x 10
y 1020
one 10
two 1020.0f
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 27
Pass-By-Value Scheme - 3
C
State of
Memory
C,The values of
parameters are
changed.
After is executedC
public void myMethod( int one,float
two )
{
one = 25;
two = 35.4f;
}
Code
x = 10;
y = 20;
tester.myMethod( x,y );
x 10
y 1020
one 1025
two 1035.4f
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 28
Pass-By-Value Scheme - 4
Code
D
State of
Memory
D,Parameters are
erased,Arguments
remain unchanged.
At after myMethodD
public void myMethod( int one,float
two )
{
one = 25;
two = 35.4f;
}
x = 10;
y = 20;
tester.myMethod( x,y );
x 10
y 1020
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 29
Arguments & Parameters,Points to Remember
1,Arguments are passed to a method using the pass-by-value scheme.
2,Arguments are matched to the parameters from left to right,The data type of an argument must be assignment compatible
to the data type of the matching parameter,
3,The number of arguments in the method call must match the number of parameters in the method definition.
4,Parameters and arguments do not have to have the same name.
5,Local copies,which are distinct from arguments,are created even if the parameters and arguments share the same name,
6,Parameters are input to a method,and they are local to the method,Changes made to the parameters will not affect the
value of corresponding arguments.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 30
Sample Program,Using an Instantiable Class
Problem Statement
Write a loan calculator program that computes both
monthly and total payments for a given loan amount,
annual interest rate,and loan period.
Major Tasks
1,Get three input values
2,Compute the monthly and total payments
3,Output the results
Key Formula
L – loan amount
R – monthly interest rate
N – number of payments
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 31
Program Design
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 32
LoanCalculator Class
Design 2
Design 1
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 33
Loan Calculator – Development Steps
1,Start with the main class and a skeleton of the LoanCalculator class,The skeleton LoanCalculator class
will include only an object/variable declaration and a constructor to create objects,
2,Implement the getInput method of LoanCalculator to accept three input values.
3,Implement the displayOutput method of LoanCalculatorto display the results.
4,Implement the computePayment method of LoanCalculator to compute the monthly and total
payments.
5,Implement the describeProgram method of LoanCalculator to display a brief description of the
program.
Chapter 4
Defining Instantiable Classes
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 2
Chapter 4 Objectives
After you have read and studied this chapter,you
should be able to
Define an instantiable class with multiple methods and a
constructor.
Differentiate the local and instance variables.
Define and use value-returning methods.
Distinguish private and public methods.
Distinguish private and public data members.
Describe how the arguments are passed to the
parameters in method definitions.
Use System.out for temporary output to verify the
program code.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 3
Building Large Programs
Learning how to define instantiable classes is the first step
toward mastering the skills necessary in building large programs,
A class is instantiable if we can create instances of the class,
The MainWindow,InputBox,and OutputBox classes are all
instantiable classes while the Math class is not,
In this chapter you will learn how to define instantiable classes
and different types of methods included in the instantiable
classes.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 4
CurrencyConverter
Let’s start with an example to cover the basics of
defining instantiable classes.
In designing an instantiable class,we start with its
specification,namely,how we want the class and its
instances behave.
A CurrencyConverter object will perform a conversion
from a foreign currency and the U.S,dollar.
What would be the most natural way for us to
interact with CurrencyConverter objects?
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 5
fromDollar and toDollar Methods
We would like to have (at least) two methods for
conversion,fromDollar and toDollar.
CurrencyConverter yenConverter;
yenConverter = new CurrencyConverter();
double amountInYen
= yenConverter.fromDollar( 500);
double amountInUS
= yenConverter.toDollar(15000);
Converting
$500 US to yen.
Converting
15,000 yen to
US dollar.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 6
setExchangeRate Methods
Since the exchange rate fluctuates,we need a
method to set the exchange rate.
CurrencyConverter yenConverter;
yenConverter = new CurrencyConverter;
yenConverter.setExchangeRate( 106.55);
$1.00 US = 106.55 yen
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 7
Using Multiple Instances
Once the CurrencyConverter class is defined,we can
use its multiple instances.
CurrencyConverter yenConverter,markConverter;
double amountInYen,amountInMark,amountInDollar;
yenConverter = new CurrencyConverter();
yenConverter.setExchangeRate(130.77);
markConverter = new CurrencyConverter( );
markConverter.setExchangeRate(1.792);
amountInYen = yenConverter.fromDollar( 200 );
amountInMark = markConverter.fromDollar( 200 );
amountInDollar = yenConverter.toDollar( 10000 );
amountInMark = markConverter.fromDollar(amountInDollar);
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 8
Template for Class Definition
class
{
}
.,,
Import Statement
Class Comment
Describe the class in
the javadoc format.
Class Name
Declarations
Declare data members
shared by multiple
methods here.
Methods
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 9
The CurrencyConverter Class
/**
* This class is used to do the currency conversion
* between a foreign currency and the U.S,dollar.
*
* @author Dr,Caffeine
*/
class CurrencyConverter
{
/**
* how much $1.00 U.S,is worth in the foreign currency
*/
private double exchangeRate;
//method declarations come here
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 10
Method Declaration
<modifier> <return type> <method name> ( <parameters> )
{
<statements>
}
public void setExchangeRagte ( double rate )
{
exchangeRate = rate;
}
Statements
Modifier Return Type Method Name Parameter
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 11
Value-Returning Method
We call a method that returns a value a value-
returning method,or non-void method.
A value-returning method must include a return
statement in the following format:
return <expression> ;
public double toDollar( double foreignMoney )
{
return (foreignMoney / exchangeRate);
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 12
Method Header Comment in javadoc
/**
* Converts a given amount in dollars into
* an equivalent amount in a foreign currency.
*
* @param dollar the amount in dollars to be converted
*
* @return amount in foreign currency
*/
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 13
Constructors
A constructor is a special method that is executed
when a new instance of the class is created.
The purpose of the constructor is to initialize an
object to a valid state,Whenever an object is created,
we must ensure that it is created in a valid state by
properly initializing all data members in a constructor.
The name of a constructor must be the same as the
name of the class.
If no constructor is defined for a class (e.g.,the
original CurrencyConverter class),then the Java compiler will include a default constructor,
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 14
Default Constructor
The default constructor will have the following form,
public <class name> ( ){
}
public CurrencyConverter( )
{
}
A default constructor has
no statements in its
method body.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 15
Defining Constructors
A constructor will have the following form,
public <class name> ( <parameters ){
<statements>
}
public CurrencyConverter( double rate )
{
exchangeRate = rate;
}
This constructor
ensures that the value
for exchangeRate is
set when a new
instance is created.
Statements
Modifier Class Name Parameter
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 16
Multiple Constructors
A class can include multiple constructors without any
problem,as long as the constructors defined for the
class have either
A different number of parameters
Different data types for the parameters if the
number of parameters is the same
public MyClass( int value ) { … }
public MyClass( ) { … }
public MyClass( float value ) { … }
These constructors will
not conflict with each
other,and therefore,valid.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 17
Visibility Modifiers,public and private
The modifiers public and private designate the
accessibility of data members and methods.
If a class component (data member or method) is
declared private,no outside methods can access it.
If a class component is declared public,any outside
method can access it.
class Test
{
public int memberOne;
private int memberTwo;
}
Test myTest = new MyTest();
myTest.memberOne = 10;
myTest.memberTwo = 20;
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 18
Data Members Should Be private
Declare the data members (class and instance
variables) private to ensure the integrity of the class.
Data members are the implementation details of the
class,and they should be kept invisible from the
outside by declaring them private.
If a data member is declared public,then we cannot
make changes to the data member without affecting
all the classes that made direct access to this data member.
Constants can (should) be declared public if they are meant to be used directly by the outside methods.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 19
Local Variables
We covered instance and class variables that are
shared among the methods of the class.
A local variable is a variable that is declared within a
method declaration.
Local variables are accessible only from the method
in which they are declared.
Memory space for local variables are allocated only
during the execution of the method,When the
method execution completes,memory space will be
deallocated.
The parameters of a method are local to the method.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 20
Sample Method
public double fromDollar( double dollar )
{
double amount,fee;
fee = exchangeRate - feeRate;
amount = dollar * fee;
return amount;
}
Parameter
Local
Variables
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 21
Memory Allocation for Local Variables - 1
Code
State of
Memory
amt
= yenConverter.fromDollar( 200 );
public double fromDollar( double
dollar )
{
double amount,fee;
fee = exchangeRate - feeRate;
amount = dollar * fee;
return amount;
}
A
A,Local variables do
not exist before the
method execution
At before fromDollarA
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 22
Memory Allocation for Local Variables - 2
Code
amt
= yenConverter.fromDollar( 200 );
public double fromDollar( double
dollar )
{
double amount,fee;
fee = exchangeRate - feeRate;
amount = dollar * fee;
return amount;
}
B
State of
Memory
B,Memory space is
allocated for the local
variables and parameter.
After is executedB
dollar
amount
200.0
fee
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 23
Memory Allocation for Local Variables - 3
Code
amt
= yenConverter.fromDollar( 200 );
public double fromDollar( double
dollar )
{
double amount,fee;
fee = exchangeRate - feeRate;
amount = dollar * fee;
return amount;
}
C
State of
Memory
C,Computed values
are assigned to the local
variables.
After is executedC
dollar
amount
200.0
fee
24846.3
124.2315
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 24
Memory Allocation for Local Variables - 4
Code
amt
= yenConverter.fromDollar( 200 );
public double fromDollar( double
dollar )
{
double amount,fee;
fee = exchangeRate - feeRate;
amount = dollar * fee;
return amount;
}
D
State of
Memory
D,Memory space is
deallocated upon exiting
the fromDollar method.
At after fromDollarD
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 25
Pass-By-Value Scheme - 1
State of
Memory
public void myMethod( int one,float
two )
{
one = 25;
two = 35.4f;
}
A
A,Local variables do
not exist before the
method execution
At before myMethodA
Code
x = 10;
y = 20;
tester.myMethod( x,y );
x 10
y 1020
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 26
Pass-By-Value Scheme - 2
State of
Memory
B,The values of
arguments are copied
to the parameters.
Values are copied at B
public void myMethod( int one,float
two )
{
one = 25;
two = 35.4f;
}
Code
x = 10;
y = 20;
tester.myMethod( x,y ); B
x 10
y 1020
one 10
two 1020.0f
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 27
Pass-By-Value Scheme - 3
C
State of
Memory
C,The values of
parameters are
changed.
After is executedC
public void myMethod( int one,float
two )
{
one = 25;
two = 35.4f;
}
Code
x = 10;
y = 20;
tester.myMethod( x,y );
x 10
y 1020
one 1025
two 1035.4f
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 28
Pass-By-Value Scheme - 4
Code
D
State of
Memory
D,Parameters are
erased,Arguments
remain unchanged.
At after myMethodD
public void myMethod( int one,float
two )
{
one = 25;
two = 35.4f;
}
x = 10;
y = 20;
tester.myMethod( x,y );
x 10
y 1020
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 29
Arguments & Parameters,Points to Remember
1,Arguments are passed to a method using the pass-by-value scheme.
2,Arguments are matched to the parameters from left to right,The data type of an argument must be assignment compatible
to the data type of the matching parameter,
3,The number of arguments in the method call must match the number of parameters in the method definition.
4,Parameters and arguments do not have to have the same name.
5,Local copies,which are distinct from arguments,are created even if the parameters and arguments share the same name,
6,Parameters are input to a method,and they are local to the method,Changes made to the parameters will not affect the
value of corresponding arguments.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 30
Sample Program,Using an Instantiable Class
Problem Statement
Write a loan calculator program that computes both
monthly and total payments for a given loan amount,
annual interest rate,and loan period.
Major Tasks
1,Get three input values
2,Compute the monthly and total payments
3,Output the results
Key Formula
L – loan amount
R – monthly interest rate
N – number of payments
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 31
Program Design
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 32
LoanCalculator Class
Design 2
Design 1
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 4 - 33
Loan Calculator – Development Steps
1,Start with the main class and a skeleton of the LoanCalculator class,The skeleton LoanCalculator class
will include only an object/variable declaration and a constructor to create objects,
2,Implement the getInput method of LoanCalculator to accept three input values.
3,Implement the displayOutput method of LoanCalculatorto display the results.
4,Implement the computePayment method of LoanCalculator to compute the monthly and total
payments.
5,Implement the describeProgram method of LoanCalculator to display a brief description of the
program.
