An Object-Oriented Approach to Programming Logic and Design Chapter 3 Using Methods and Parameters.

An Object-Oriented Approach to An Object-Oriented Approach to

Programming Logic and DesignProgramming Logic and Design

Chapter 3Using Methods and Parameters

An Object-Oriented Approach to Programming Logic and Design 2

ObjectivesObjectives

• Create methods with and without arguments• Create instance methods in a class• Explore the rationale behind data hiding• Organize classes


Objectives (continued)Objectives (continued)

• Understand the role of the this reference• Begin to understand how to use constructors


Creating Methods With and Without Creating Methods With and Without ArgumentsArguments

• Method – a program module containing statements that carry out a task

• Invoking, or calling, a method causes it to execute

• A method may require that data items (called arguments or parameters) be provided to it

• A method may or may not send back data (called a return value)


Creating Methods With and Without Creating Methods With and Without Arguments (continued)Arguments (continued)

Example: a class with no arguments and no return value


Creating Methods With and Without Creating Methods With and Without Arguments (continued)Arguments (continued)

• Method declaration (header) contains:– Optional access modifiers (public, private, or

protected)

– Return type

– Method name

– Optional list of arguments, separated by commas


Creating Methods With No ArgumentsCreating Methods With No Arguments

• Creating methods with no arguments:– Place the method within the class that will use it,

but not within any other method


Creating Methods With No Arguments Creating Methods With No Arguments (continued)(continued)

Invoking a method with no arguments



Program flow in a method call





• Full name of a method:

<class name>.<method name>

Example:

Hello.nameAndAddress()


Creating Methods With One ArgumentCreating Methods With One Argument

• Requires the following in the method header:– The type of the argument

– A local name for the argument

• Argument receives a value that is passed in when the method is invoked

• Any method that does not return a value is declared with type void


Creating Methods With One Argument Creating Methods With One Argument (continued)(continued)



• When calling a method with arguments, you can pass – Values

– Variables

– Constants

• Each time a method is called, it is reinitialized to use the new values for arguments that are passed in the call






Creating Methods With Multiple Creating Methods With Multiple ArgumentsArguments

• Creating methods with multiple arguments:– Argument list is separated by commas

– Each argument’s type is specified with the argument name, even if two or more arguments are the same type

– Argument type is placed before the argument name


Creating Methods With Multiple Creating Methods With Multiple Arguments (continued)Arguments (continued)

Method with two arguments


Creating Methods With Multiple Creating Methods With Multiple ArgumentsArguments (continued)(continued)


Creating Methods With Multiple Creating Methods With Multiple Arguments (continued)Arguments (continued)

• Arguments passed to a method must match the method’s declaration in: – Number of arguments

– Type of each argument

– Order of each argument in the list


Creating Methods that Return ValuesCreating Methods that Return Values

• Return type can be any type• If no value is to be returned, the type is void• Return type is placed in the header before the

method name

Example:public static numeric predictRaise(numeric money)


Creating Methods that Return Values Creating Methods that Return Values (continued)(continued)

• Method can only return at most one value• Return value can be assigned to a variable by

using the method call as a variable

Example:

myNewSalary = predictRaise(mySalary)


Creating Methods that Return Values Creating Methods that Return Values (continued)(continued)

• Return value of a method can be used as a variable

Example:print “New salary is”, predictRaise(mySalary)


Creating Instance Methods in a ClassCreating Instance Methods in a Class

• Every object that is an instance of a class is assumed to possess the same methods as the class

• Static methods: methods for which no object needs to exist

• Non-static methods: methods that exist to be used with an object created from a class


Creating Instance Methods in a Class Creating Instance Methods in a Class (continued)(continued)

• Mutator methods: methods which set values• Accessor methods: methods which retrieve values





• A class does not create an object; an object must be instantiated from the class

• Once instantiated, a class’s methods can be invoked by name

Syntax:

<object identifier>.<method name>






Exploring the Rationale Exploring the Rationale Behind Data HidingBehind Data Hiding

• Accessing data only through public methods of a class guarantees that the data will only be manipulated in an approved way

• Methods can be written to ensure that the data conforms to required standards

• Example: ensuring that all phone numbers have area codes


Organizing ClassesOrganizing Classes

• Data fields: – No special order required, but key data items

(used as database look-up values) placed first

– Common practice to declare all data items first, before any methods

• Methods:– Common practice to order them alphabetically

by name, or to put them in get/set pairs


Organizing Classes (continued)Organizing Classes (continued)


Understanding the Role Understanding the Role of the of the thisthis Reference Reference

• Just one copy of a class’s methods are stored in memory, and all objects instantiated from that class use the same stored method

• Each object has its own set of data• The this reference (or pointer variable) allows

the programmer to specify the use of the particular object instance

• The this reference is implicitly used when the object’s code is running


Understanding the Role Understanding the Role of the of the thisthis Reference (continued) Reference (continued)


An Introduction to Using ConstructorsAn Introduction to Using Constructors

• Constructor method establishes the object when it is instantiated

• Default constructor requires no arguments, and is created automatically by the compiler for every class you write

• Constructor class has the same name as the class name in some languages

• Constructors are usually declared as public so that other classes can instantiate objects of this class


An Introduction to Using ConstructorsAn Introduction to Using Constructors(continued)(continued)

• Constructor is a method; it can contain any valid program statements

• Constructor is usually placed as the first method in the class

• Constructor may have arguments that have to be supplied when creating a new object from the class


An Introduction to Using ConstructorsAn Introduction to Using Constructors(continued)(continued)


SummarySummary

• Method is a procedure that contains a series of statements to accomplish a task

• Methods may contain one or more arguments defining data that must be supplied when calling the method

• Method may return a value of a specific type, or may be void

• An instantiated object possesses the methods and attributes of the class from which it was created


Summary (continued)Summary (continued)

• Data hiding using encapsulation guarantees that the data may only be manipulated by the methods of a class

• Most data items are declared as private to support data hiding

• this reference is a pointer to the instantiated object whose code is currently running

• Constructor methods are created automatically for each class, and are executed when the object is created from the class

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An Object-Oriented Approach to Programming Logic and Design Chapter 3 Using Methods and Parameters.

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