Java/C3/Static-Methods/English

Title of script: Static Methods

Author: Joms Antony

Keywords: Static methods, Class methods, Instance methods, Static variables

Visual Cue	Narration
Slide 1	Welcome to the Spoken Tutorial on Static Methods.
Slide 2 Learning Objectives What are static methods Defining static methods Difference between instance methods and static methods How to use static methods	In this tutorial we will learn: What are static methods Defining static methods Difference between instance methods and static methods and How to use static methods
Slide 3 Software Requirements Ubuntu 14.04 JDK 1 .7 Eclipse 4.3.1	Here we are using Ubuntu 14.04 JDK 1 .7 and Eclipse 4.3.1
Slide 4 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	To follow this tutorial, 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.
Slide 5 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	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.
Slide 6 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	Let us see how to use static methods with an example. This 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.
Slide 7 Static Method Any method which is used to handle static variables can be defined as a static method If a method is used to change the value of Organisation name, then it can be defined as a static method	Any method which is used to handle static variables can be defined as a static method. Say for example, if a method is used to change the value of Organisation name, then it can be defined as a static method.
Slide 8 Instance Vs Static Methods Instance methods can access static variables A Static method can directly access and modify only static variables	Now let us explore the differences between instance method and static method. Instance methods can access static variables, whereas A static method can directly access and modify only static variables.
Slide 8(A) Instance methods are invoked only by an object A static method can be invoked directly without creating an object	Instance methods are invoked only by an object whereas A static method can be invoked directly without creating an object.
Slide 8(B) 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.	* We cannot use ‘this’ and ‘super’ keyword inside a static method. 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.
Slide 9 Static Method - Sample Code Highlight the code public static void setOrgName(String org) { orgname=org; }	Now let us look at the sample code for a static method. If the StudentEnroll class requires a method to change the value of the organisation name. It can be defined as a static method as shown. The setOrgName method represented here is a static method which can modify the value of orgname.
Slide 10 Invoking Static Methods A static method can be invoked directly by the class name itself Highlight setOrgName Highlight the full code	A static method can be invoked directly by the class name itself For Example, the setOrgName method can be invoked as StudentEnroll.setOrgName within brackets IIT Mumbai.
In Eclipse IDE, create a project StaticMethodDemo	Now we will switch to Eclipse and create a new project called StaticMethodDemo. Inside this project we will create the necessary classes to demonstrate the usage of Static methods.
Right click on src folder and click New-> Class and type the class name as StudentEnroll and hit Enter	We will create a new class StudentEnroll.
//copy and paste the code inside the class and highlight them private String id, name; private static int count; private static String orgname="IIT Bombay";	Now type the following code to represent the StudentEnroll class.
Highlight static int count and static String orgname Highlight static String orgname Highlight static String orgname="IIT Bombay";	Note that there are two static variables count and orgname. Also note that orgname is not a static constant rather it is normal static variable The static variable orgname is initialized as “IIT Bombay”
click on Source -> and select Generate Constructor using Fields	Now click on Source -> and select Generate Constructor using Fields
Delete the super keyword	Delete the super keyword from the generated code.
Inside the constructor, type count++;	Inside the constructor, type count ++ semicolon So, the count value is incremented every time an object is created.
Type public void showData() //copy the code and highlight it { System.out.println(id+" "+name+" "+orgname); }	Now we will add a method showData( ) to this class to print the values of the variables. So type public void showData( ). Within brackets type the following code to print the values of id, name and organisation name.
//copy and paste the code public static void setOrgName(String org) { orgname=org; }	Now we will add the static method setOrgName which can change the value of orgname. Type the following code. We have already seen this code earlier in a slide.
Inside this static method type id = “newid”;	Let us see what happens if we try to access an instance variable directly inside this static method. Type, id= “newid” semicolon
Hover the cursor to show the error	Now an error comes up in eclipse. It indicates that an instance variable cannot be accessed directly inside a static method.
Comment the statement	So let us comment this line and proceed.
//Copy and paste the code and highlight according to narration public static void showOrgData() { System.out.println("\nORGANISATION DATA"); System.out.println("Name:"+orgname); System.out.println("Total Students Enrolled:"+count); }	Now we will add one more static method showOrgData. These statements print the values of orgname and count.
click new-> class and then type name as Demo.	Now right click on the default package click new-> class and then type the name as Demo. Inside this class we will have the main method, So type main and then press ctrl+space to generate the main method.
//Copy the code to create objects 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();	We will create a few objects of StudentEnroll class to represent student enrollments. 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.
Click on run button	Now let us run the Demo program.
Highlight 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	We can see that the values of the variables corresponding to s1 i.e IT101, ADIL and IIT BOMBAY gets printed. 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.
Type 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.
Click on run button	Now run the Demo program again.
Box IIT Mumbai	We can see that the organisation name is changed to “IIT Mumbai”.
Switch to slides	Let us come back to slides.
Slide 11 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.	Object references can be passed to a static method. This way a static method can access the instance variables of that particular object.
Switch to Eclipse Go to StudentEnroll class	Let us try it in our code. Switch to Eclipse and go to the StudentEnroll class.
In the setOrgName method After String org, type comma StudentEnroll s uncomment id = "newid" Type s.id="newid";	Now in the setOrgName method, pass another argument as an object of StudentEnroll class. So after String org, type comma StudentEnroll s Now inside this method, uncomment id = "newid" And instead of id, type s.id
Go to the Demo class	Now go to the Demo class.
In the StudentEnroll.setOrgName("IIT Mumbai"); after “IIT Mumbai”, type comma s1	Let us modify the function call to setOrgName method by passing the StudentEnroll object s1. So here, after “IIT Mumbai”, type comma s1.
Click on run button	Now run the Demo program again.
Highlight id “newid”	We can see that the value of id for s1 has changed to “newid”
Slide 12 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	Let us summarize. 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
Slide 13 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” )	For the Assignment, 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
Slide 13 A 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	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 Also define a method show( ) to print all the car details
Slide 13 B 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” )	As before, We need to perform the following as listed Note that we have to identify and define the static method as required
Slide 13 C 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	Also create a Demo class. 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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Contributor slide (retain the slide as in TEX file)	This script has been contributed by: Dept. of Information Technology, Amal Jyothi College of Engineering. This is Priya from IIT Bombay, thanks for joining.

Contributors and Content Editors

Nancyvarkey, Priyacst