Difference between revisions of "Java/C3/Static-Variables/English-timed"
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| − | |Here, we are using: '''Ubuntu 12.04''', | + | |Here, we are using: |
| + | '''Ubuntu 12.04''', | ||
'''JDK 1.7 '''and | '''JDK 1.7 '''and | ||
| + | |||
'''Eclipse 4.3.1''' | '''Eclipse 4.3.1''' | ||
Latest revision as of 14:34, 5 December 2019
| 00:01 | Welcome to the Spoken Tutorial on Static Variables. |
| 00:05 | In this tutorial, we will learn about: What are static variables, |
| 00:10 | creating static variables and how to use static variables. |
| 00:17 | Here, we are using:
Ubuntu 12.04, JDK 1.7 and Eclipse 4.3.1 |
| 00:27 | To follow this tutorial, you must have knowledge of basics of Java and Eclipse IDE. |
| 00:35 | You should also have the knowledge of classes, objects and instance variables in Java. |
| 00:42 | If not, for relevant Java tutorials, please visit the link shown. |
| 00:49 | A static variable is a variable which is associated with the entire class. |
| 00:55 | It is also called a class variable. |
| 00:58 | It is declared using the static keyword. |
| 01:02 | We have seen about static variable briefly in the earlier tutorial. |
| 01:08 | In this tutorial, we will see it in detail. |
| 01:11 | Now, we will switch to Eclipse and create a new project called StaticVariableDemo. |
| 01:18 | Inside this project, we will create the necessary classes to demonstrate the usage of Static variables. |
| 01:26 | So, right-click on src folder and click New > Class and type the name of the class as StudentEnroll and press Enter. |
| 01:37 | Let us illustrate the usage of static variables with an example. |
| 01:42 | Consider a class created to represent student enrollments in an organisation. |
| 01:49 | This class contains the Name, Id , Branch and Total Count of students enrolled. |
| 01:56 | Now, let us visualize what happens when student enrollments are done. |
| 02:02 | By default, Total Count is 0. The Name of the first student is ADIL. |
| 02:09 | Id is IT101, Branch is IT. |
| 02:14 | Now the Total Count is updated as 1. |
| 02:18 | Similarly when the second student AMAL gets enrolled, Total Count is updated to 2. |
| 02:25 | When the third student CAROL gets enrolled, Total Count is updated to 3. |
| 02:32 | Now we can identify that the variable Total Count is common to all the objects and has a single value. |
| 02:40 | So, the variable Total Count can be represented as a static variable. |
| 02:45 | We can also see that the variables Name, Id and Branch have their own copies for each object. |
| 02:54 | Also they have specific values for each object. |
| 02:59 | So, these variables can be treated as instance variables. |
| 03:04 | Now, let us look at the code representing the student Enroll class. |
| 03:09 | The instance variables are declared as id, name and branch. |
| 03:16 | The variable count is declared as static since it is common to the whole class. |
| 03:22 | When a class is loaded, a static variable occupies a single fixed memory location. |
| 03:28 | Whereas Instance variables of each object occupy separate memory locations. |
| 03:35 | Now click on Source > and select Generate Constructor using Fields. |
| 03:41 | Delete the super keyword from the generated code. |
| 03:45 | This constructor can initialise the values of the id, name and branch fields. |
| 03:51 | We also need to increment the value of the variable count by one every time an object is created. |
| 03:59 | So, inside the constructor, type: count ++ semicolon. |
| 04:05 | Now we will add a method showData( ) to this class, to print the values of all the variables. |
| 04:13 | So, type public void showData( ) within brackets type the following code to print the values of id, name, branch, and total number of students enrolled. |
| 04:27 | Now right-click on the default package and click on New > Class and then type name as Demo. |
| 04:36 | Inside this class, we will have the main method. |
| 04:39 | So, type main and then press ctrl+space to generate the main method. |
| 04:46 | Now we need to print the Student Enrollment data. |
| 04:50 | We will create a few objects of StudentEnroll class to represent student enrollments. |
| 04:57 | So, type the following code: StudentEnroll s1 equals new StudentEnroll. |
| 05:04 | Now we can pass the values of different arguments. |
| 05:08 | Within brackets, type IT101 as id, ADIL as name and IT as branch. |
| 05:17 | Now let us invoke the showData method to print the enrollment details. |
| 05:22 | So, type: s1.showData( ). Now run the Demo program. |
| 05:29 | We can see that the values of the instance variables corresponding to s1 get printed. |
| 05:36 | Also note that the value of the number of student enrollments is 1. |
| 05:42 | This is because we have created only 1 object. |
| 05:47 | Now type the following code to create one more object s2. |
| 05:52 | The showData method can be called once again using s2. |
| 05:56 | Again run the Demo Program. |
| 05:59 | We can see that the values of the instance variables corresponding to s2 get printed. |
| 06:06 | Also, note that the value of number of student enrollments is updated to 2 for both s1 and s2. |
| 06:14 | Now create one more object s3. |
| 06:18 | Now let us Invoke the showData method again using s3. |
| 06:23 | Run the Demo program again. |
| 06:26 | We can see that the values of instance variables corresponding to s3 get printed. |
| 06:32 | Also note that the value of number of student enrollments is now updated to 3 in all the cases. |
| 06:41 | Now we can understand that value of number of student enrollments is common to all the objects. |
| 06:48 | Come back to slides. |
| 06:51 | The static modifier is also used along with the final modifier. |
| 06:56 | It is done to define a constant which is common to the entire class. |
| 07:01 | Conventionally, the names of such constant variables are spelt in uppercase letters. |
| 07:08 | Now come back to eclipse. |
| 07:11 | Open the StudentEnroll class and type the variable declaration as public static final String ORG_NAME = “IITB”; |
| 07:23 | As an example, if all the students are getting enrolled to the same organisation, say IITB. |
| 07:31 | It can be represented by using a constant static variable say ORG_NAME. |
| 07:38 | If the name is composed of more than one word, the words are separated by an underscore. |
| 07:44 | Usually we declare such constants with a public visibility. |
| 07:49 | Now go to the Demo class and type the following code. |
| 07:55 | Here you can see that ORG_NAME is accessed by using its class name StudentEnroll. |
| 08:03 | Now run the Demo program again. |
| 08:06 | We can see that the ORGANISATION name is getting printed as IITB. |
| 08:11 | Let us summarize. In this tutorial, we have learnt about: |
| 08:17 | What is a static variable and when it is used |
| 08:21 | How to create and invoke the static variables. |
| 08:25 | As an Assignment, design a class CarService to represent a car service station. |
| 08:32 | This class should contain variables to represent the following details: Name of the Service Station, |
| 08:39 | Car make, model and register number - which are in for service |
| 08:44 | No. of Cars in for Service. |
| 08:47 | Identify the instance variables and static variables. |
| 08:51 | Declare them using suitable keywords. |
| 08:55 | Define a constructor to initialise the values for Car make, model and register number. |
| 09:01 | Define a method show( ) to print the values of all the variables. |
| 09:07 | Also, create a Demo class containing the main method to verify the results
i.e create a few objects of CarService. |
| 09:16 | Invoke the show( ) method using these objects. |
| 09:20 | Also, access the static variables directly using the class name. |
| 09:25 | The video at the following link summarizes the Spoken Tutorial Project. Please download and watch it. |
| 09:32 | The Spoken Tutorial Project Team: Conducts workshops using spoken tutorials and
Gives certificates on passing the online tests. |
| 09:41 | For more details, please write to us. |
| 09:45 | Spoken Tutorial Project is funded by the NMEICT, MHRD, Government of India. |
| 09:51 | More information on this mission is available at the link shown. |
| 09:56 | This script has been contributed by: Department of Information Technology, Amal Jyothi College of Engineering. |
| 10:03 | This is Priya from IIT Bombay, signing off. Thanks for joining. |
