java methods part1

8/4/2019 Java Methods Part1

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Methods:Making Your Application Modular.

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


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OverviewOverview

In 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


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What is a method?What is a method?What is a method?


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Java MethodsJava Methods

In Java, a methodis a block of statements that has aname and can be executed by callingit from someother place in your program.

You have already been using methods. For example:

to print text to the console, you use the println or printmethods.

to get an integer from the user, you use the nextIntmethod.

and the granddaddy of all methods,main.

With the exception ofmain, all the methods youve

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

Themain method belongs to the class defined by

your application.


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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 same

program.

Promotes code-reusability in later programs


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Modular DesignModular Design

public class MyClass

{ public static void main(String[] args){

statement;statement;

statement;statement;statement;statement;


statement;


}

}

Here is an example of non-modular design


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Modular DesignModular Design

public class MyClass{

public static void main(String[] args){


public static void doTask1( ){

}

public static void doTask2( ){

}

statement;statement;statement;statement;

statement;statement;statement;

doTask1();

doTask2();


}}

This is an example of a modular design usingmethods


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The Basics of Making a MethodThe 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.

Heres the basic form for a method declaration,

at least for the types of methods we have seen sofar:

This method can

be seen byother classes.

This method can exist even if no

objects are created from thisclass. Will explain this more later.

The data type of thevalue returned by the

method when it endsThe name of

this method.

Lists what can be

passed to the method

.

The body of the

method


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Before We Get DeeperBefore We Get Deeper

To promote software reusability:

every method should be limited to performing a single,

well-defined task.

the name of the method should express that task

effectively.

A small method that performs one task is easier to

test and debug than a larger method that performsmany tasks.

If you cannot choose a concise name that

expresses a methods task, your method might beattempting to perform too many diverse tasks. It isusually best to break such a method into severalsmaller method declarations.


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Declaring Methods in Your ClassDeclaring Methods in Your Class

public class MyClass{



}

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

{statement;statement;

}

//----------------------------------------------

public static double dosomethingElse( double num1){statement;statement;

}}


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


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Calling a MethodCalling a Method

To call (or execute) a method, use themethod name followed by () and ;

printMsg(); // doesnt take parameters

When called, program executes the body ofthe called method.

After the method terminates, executionresumes in the calling method (for example

the main) at the point of call. The main can call any number of methods

Methods can call other methods.


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ExampleExample

public class HelloWorldMethod{


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();}

}

Execution

starts at main


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Methods that Take ParametersMethods that Take ParametersMethods that Take Parameters


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Methods that Accept ParametersMethods that Accept Parameters

A parameteris a value that you can pass to amethod.

The method can then use the parameter as if it were alocal variable initialized with the value of the variablepassed to it by the method call.

A method that accepts parameters must list the

parameters in the method declaration.

The parameters are listed in a parameter list thatsin the parentheses that follow the method name.

For each parameter used by the method, you list theparameter type followed by the parameter name.

If you need more than one parameter, you separate

them with commas.

java methods part1

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