Difference between revisions of "Java/C3/Static-Methods/English"

Learning Objectives

• What are static methods
• Defining static methods
• Difference between instance methods and static methods
• How to use static methods

• What are static methods
• Defining static methods
• Difference between instance methods and static methods and
• How to use static methods

Software Requirements

• Ubuntu 14.04
• JDK 1 .7
• Eclipse 4.3.1

• Ubuntu 14.04
• JDK 1 .7 and
• Eclipse 4.3.1

Prerequisites

• Basic knowledge of Java and Eclipse IDE
• Knowledge of instance variables, methods and static variables in Java
• For relevant tutorials, please visit http://www.spoken-tutorial.org

You must have knowledge of basics of Java and Eclipse IDE.

You should also have the knowledge of instance variables, methods and static variables in Java.

If not, for relevant Java tutorials, please visit the link shown.

Static Method

• A static method is a method which is associated with the entire class

• It is also called a class method and is declared using the static keyword.

• Static methods are usually used to handle static variables

It is also called a class method and is declared using the static keyword.

Static methods are usually used to handle static variables.

Inside this project we will create the necessary classes to demonstrate the usage of Static methods.

Static Method – Example

Show the final shot in the slide.

(Three students enrolled and total count as 3)

Highlight name and id

Highlight organization and total count

The example is very similar to the one which is used in the Static Variable tutorial.

Here again we are representing the StudentEnroll class.

Recall that the variables name and id are handled as instance variables.

Here the variables organization and total count are common to the entire class.

So they can be treated as static variables.

private String id, name;

private static int count;

private static String orgname="IIT Bombay";

Highlight static String orgname

Highlight static String orgname="IIT Bombay";

Also note that orgname is not a static constant rather it is normal static variable.

The static variable orgname is initialized as “IIT Bombay”.

count ++ semicolon

So, the count value is incremented every time an object is created.

public void showData()

//copy the code and highlight it

{

System.out.println(id+" "+name+" "+orgname);

}

So type public void showData( ).

Within brackets type the following code to print the values of id, name and organisation name.

public static void setOrgName(String org)

{

orgname=org;

}

Type the following code.

The setOrgName method represented here is a static method which can modify the value of orgname.

Any method which is used to handle static variables can be defined as a static method.

Instance Vs Static Methods

• Instance methods can access static variables
• A Static method can directly access

and modify only static variables

Instance methods can access static variables, whereas

A static method can directly access and modify only static variables.

• Instance methods are invoked only by an object
• A static method can be invoked

directly without creating an object

A static method can be invoked directly without creating an object.

• We cannot use ‘this’ and ‘super’

keyword inside a static method.

• These keywords refer to the instance of a particular class.
• In a static context we can’t refer to instances of a class.

• This is because these keywords refer to the instance of a particular class.
• In a static context we can’t refer to instances of a class.

id = “newid”;

Type,

id= “newid” semicolon

It indicates that an instance variable cannot be accessed directly inside a static method.

public static void showOrgData()

{

System.out.println("\nORGANISATION DATA");

System.out.println("Name:"+orgname);

System.out.println("Total Students Enrolled:"+count);

}

These statements print the values of orgname and count.

Inside this class we will have the main method,

So type main and then press ctrl+space to generate the main method.

StudentEnroll s1=new StudentEnroll("IT101","ADIL");

StudentEnroll s2=new StudentEnroll("CS101","AMAL");

StudentEnroll s3=new StudentEnroll("CS101","CAROL");

(Copy the code)

s1.showData();

s2.showData();

s3.showData();

(Copy and paste)

StudentEnroll.showOrgData();

So type the following code to create 3 objects s1, s2 and s3.

Now let us invoke the showData method to print the enrollment details.

Type the following code to invoke showData method on s1, s2 and s3.

Let us also invoke the method showOrgData to print the values of orgname and count.

Since it is a static method we can invoke it directly using its class name.

To do so, type this code.

IT101 ADIL IIT Bombay

Highlight CS101 AMAL IIT Bombay

CS101 CAROL IIT Bombay

Box IIT BOMBAY

Highlight Name:IIT Bombay

Highlight Total Students Enrolled:3

Similarly the values corresponding to s2 and s3 are also printed.

Note that the value of orgname ie IIT BOMBAY is common for s1, s2 and s3.

orgname and count are printed separately by the static method showOrgData.

Note that the organisation name is printed as IIT Bombay.

The value of the number of student enrollments is printed as 3, as we have already created 3 objects.

StudentEnroll.setOrgName("IIT Mumbai");

(Copy the code)

s1.showData();

s2.showData();

s3.showData();

Type

StudentEnroll.showOrgData();

Now let us invoke the static method setOrgName.

We will change the organisation name from “IIT Bombay” to “IIT Mumbai”.

So type the following code.

Now let us once again invoke the showData method on s1, s2 and s3 to print the enrollment details.

For that type the following code again.

Once again, let us invoke the method showOrgData to print the values of orgname and count.

To do so, type this code.

Passing an object reference

• Object references can be passed to a

static method.

• This way a static method can access

the instance variables of that particular object.

This way a static method can access the instance variables of that particular object.

Go to StudentEnroll class

Switch to Eclipse and go to the StudentEnroll class.

After String org, type

comma StudentEnroll s

uncomment id = "newid"

Type s.id="newid";

So after String org, type

comma StudentEnroll s

Now inside this method, uncomment id = "newid"

And instead of id, type s.id

after “IIT Mumbai”, type comma s1

So here, after “IIT Mumbai”, type comma s1.

Summary

• What is a static method and when it is used
• How to differentiate static methods and instance methods
• How to create and invoke static methods

In this tutorial we have learnt about

• What is a static method and when it is used
• How to differentiate static methods and instance methods and
• How to create and invoke static methods

• Design a class CarService to represent

a Car Service Station

• This class should contain variables to

represent the following

• Name of the Service Station
• Car make, model, regno and status
• No of Cars in for Service
• No of cars out after Service

( Highlight “status” )

( Highlight “No of cars out after service” )

This assignment is a continuation of the static variable assignment.

Make sure that you have completed the Static variable assignment.

We will highlight only the modifications here.

Here we have a variable to represent “status”.

It is used to indicate whether the car is “in” for service or “out” after service

We will also have another variable to represent

No of cars out after Service

• Define a method service( Car c)

which updates the status to ”out”

Accordingly it modifies the values for

• No of Cars in for Service
• No of Cars out after Service

• Define a method show( ) to print the

car details

Accordingly it modifies the values for

• No of Cars in for Service
• No of Cars out after Service

Also define a method show( ) to print all the car details.

• Identify the instance variables and

static variables

• Also Identify the instance methods and static methods

• Define a constructor to initialise the

values for Car make, model, regno and status

( Highlight “static method” )

We need to perform the following as listed

Note that we have to identify and define the static method as required.

• Also create a Demo class containing

the main method

Inside the main method

• Create a few objects of CarService

• Invoke the service( ) method on some

of them

• Invoke the show( ) method using all the objects and verify the results

Inside the main method,

Create a few objects of CarService.

Invoke the service( ) method on some of them.

Invoke the show( ) method using all the

objects and verify the results.

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Please download and watch it.

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• Conducts workshops using spoken tutorials and

• Gives certificates on passing the online tests

For more details, please write to us.

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More information on this Mission is available at the link shown.

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Dept. of Information

Technology, Amal Jyothi College of Engineering.

This is Priya from IIT Bombay, thanks for joining.