Methods for Making Application Modular in Computer Programming | CS 140, Study notes of Computer Science

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Methods:Methods:^ Methods:Making Your Application Modular.Making Your Application Modular.Making Your Application Modular.

Overview^ OverviewIn these chapters you will learn:^ ‰

What is a method?

Declaring methods.

Using (or calling) methods.

Writing methods that take parameters.

Writing methods that return values

Declaring variables in the method.^ „

Scope of variables.

Method overloading

Java Methods^ Java Methods ‰

In Java, a

method is a block of statements that has a

name and can be executed by

calling it from some

other place in your program.

You have already been using methods. For example:^ „

to print text to the console, you use the

println

or

print

methods.

to get an integer from the user, you use the

nextInt

method.

and the granddaddy of all methods,

main

With the exception of

main

, all the methods you’ve

used so far have been methods that are defined bythe Java API and that belong to a particular Javaclass.

The

main

method belongs to the class defined by

your application.

Why Do We Need Methods?^ Why Do We Need Methods?^ ‰

Modular programming: breaking a programup into smaller, manageable modules or“methods”.

Motivation for modular programming:^ „

Simplifies the process of writing programs

Enables a divide-and-conquer approach

Improves maintainability of programs

Prevents repeating code within the sameprogram.

Promotes code-reusability in later programs

Modular Design^ Modular Design public class MyClass{

public static void main(String[] args){

statement;statement;

public static void doTask1( ){ } public static void doTask2( ){ }

statement;statement;statement;statement; statement;statement;statement;

doTask1();doTask2();statement;statement;

} }

This is an example of a modular design usingmethods

The Basics of Making a Method^ The Basics of Making a Method

public static return-type method-name( parameter-list ){

statements...

All methods — including the main method — mustbegin with a

method declaration.

Here’s the basic form for a method declaration,at least for the types of methods we have seen sofar:

This method canbe seen byother classes.

This method can exist even if noobjects are created from thisclass. Will explain this more later.

The data type of thevalue returned by themethod when it ends

Lists what can bepassed to the method. The name ofthis method.

The body of themethod

Declaring Methods in Your Class^ Declaring Methods in Your Class

public class MyClass{

public static void main(String[] args){

statement;statement;

} //----------------------------------------------public static int doSomething( int value){

statement;statement;

} //----------------------------------------------public static double dosomethingElse( double num1){

statement;statement;

} }

Using Your Methods: Calling a MethodUsing Your Methods: Calling a Method^ Using Your Methods: Calling a Method

Example^ Example

public class HelloWorldMethod{

public static void main(String[] args){

sayHello(); } //-------------------------------------public static void sayHello(){

System.out.println("Hello, World!"); } } public class HelloWorldMethod{

public static void sayHello(){

System.out.println("Hello, World!"); } //-------------------------------------public static void main(String[] args){

sayHello(); } }

Executionstarts at main

Methods that Take ParametersMethods that Take Parameters^ Methods that Take Parameters

Example^ Example ‰

A method that takes three numbers and displays their average.

public

static

void

dispAverage(int

num1,

int

num2,

int

num3)

{

double

average;

average

=

(double)

(num1+num2+num3)/3.0;

System.out.println("The

average

is

"+

average);

}

To call this method:

.^ .^ .^ .^

.

dispAverage(

2,

4,

5);

.^ .^ .^ .^

.

Example^ Example ‰

Putting it all together: public class AverageCalculator{

public static void main(String[] args){

dispAverage( 2, 14, 5);

} public static void dispAverage(int num1, int num2, int

num3)

double average;average = (double) (num1+num2+num3)/3.0;System.out.println("The average is "+ average);

} }

Returning Values from a Method.^ Returning Values from a Method. ‰

The real benefit of methods comes when they canperform some task and then return the result of thattask to the calling method^ „

For example, a method that take thee numbers then returntheir average to the calling method.

To create a method that returns a value:1.

simply indicate the type of that return value on the methoddeclaration in place of the void keyword. public

static

double

getAverage(int

num1,

int

num2,

int

num3)

2.

at the end of the body of the method, use the

return

statement to return the value to the calling method.

The^ The

returnreturn

Statement.Statement.

Is used to return a value from a method tothe calling method. Here is the general formof it:

return expression;

The expression must evaluate to a valuethat’s the same type as the type listed in themethod declaration.

The

return

statement is last thing that will

be executed in the method body.