Java/C3/Static-Blocks/English-timed
From Script | Spoken-Tutorial
| Time | Narration |
| 00:01 | Welcome to the Spoken Tutorial on Static blocks . |
| 00:06 | In this tutorial we will learn: What are static blocks |
| 00:10 | How to declare static blocks and How to use static blocks. |
| 00:16 | Here we are using :Ubuntu 14.04 JDK 1 .7 and Eclipse 4.3.1 |
| 00:26 | To follow this tutorial, you must have knowledge of basics of Java and Eclipse IDE. |
| 00:34 | You should also have the knowledge of instance variables, static variables and static methods in Java. |
| 00:43 | If not, for relevant Java tutorials, please visit the link shown. |
| 00:48 | Let us learn about static blocks. |
| 00:52 | A Static block is mostly used for initializing values of static variables. |
| 00:59 | A static block is declared using the static keyword. |
| 01:03 | Static blocks are executed when the class is loaded in memory. |
| 01:08 | If there are static blocks in a program, they are invoked before constructors. |
| 01:14 | We cannot access instance variables inside a static block. |
| 01:19 | Now, we will switch to Eclipse and create a new project called StaticBlockDemo. |
| 01:26 | Inside this project, we will create the necessary classes to demonstrate the usage of Static Blocks. |
| 01:33 | Right click on src folder and click New-> Class. |
| 01:38 | Type the name of the class as StudentEnroll and press Enter. |
| 01:44 | Now type the following code to represent the StudentEnroll class. |
| 01:49 | Note that there are two static variables count and orgname. |
| 01:54 | Now click on Source -> and select Generate Constructor using Fields. |
| 02:00 | Delete the super keyword from the generated code. |
| 02:04 | We want a message to be printed whenever the constructor is invoked. |
| 02:09 | So inside this constructor, type the following code to print “Constructor invoked”. |
| 02:15 | Now we will add a method showData( ) to this class to print the values of the variables. |
| 02:21 | So type the following code. |
| 02:23 | Now we will add a static block to initialize the values of count and orgname. |
| 02:29 | Type the following code. |
| 02:32 | The variables orgname and count are static variables. |
| 02:36 | This block of code within the curly brackets prefixed by the static keyword is a static block. |
| 02:42 | This static block initializes the values for count and orgname as 100 and IITM respectively. |
| 02:51 | Inside this static block, type the following code to print “static block-1 is invoked”. |
| 02:58 | Now we will add one more class containing the main method. |
| 03:03 | So right click on the default package, click New-> Class and then type the name as Demo. |
| 03:11 | Inside this class we will have the main method. |
| 03:15 | Type main and then press Ctrl+space to generate the main method. |
| 03:21 | We will create an object of StudentEnroll class. |
| 03:25 | Type the following code to create an object s1. |
| 03:29 | Now let us invoke the showData method to print the values. |
| 03:33 | Type s1.showData() semicolon |
| 03:38 | Now let us run the Demo program. |
| 03:41 | We can observe that static block is invoked before the constructor. |
| 03:46 | The values of count and orgname are initialized as defined in the static block. |
| 03:53 | Now let us go back to the StudentEnroll class. |
| 03:57 | Let us see what happens if we initialise the value of id inside the static block. |
| 04:03 | Inside the static block type, id equals IT01 semicolon |
| 04:10 | We can see that an error comes up. |
| 04:13 | It indicates that an instance variable cannot be accessed inside a static block |
| 04:19 | Now let us comment this line and proceed further. |
| 04:25 | Let us go back to the slides |
| 04:27 | A class can contain multiple static blocks. |
| 04:30 | In such a case they are called only once in the order that they appear in the source code. |
| 04:37 | Switch back to Eclipse to verify it. |
| 04:40 | Let us include one more static block after the existing one. |
| 04:45 | Type the following code. |
| 04:47 | This static block initializes the values for count and orgname as 200 and IITB respectively. |
| 04:57 | Inside this static block type the following code. |
| 05:01 | Now let us run the Demo program again. |
| 05:04 | From the output, We can verify that the second static block is invoked after the first. |
| 05:10 | The values of the static variables count and orgname are updated by the second static block. |
| 05:18 | They are 200 and IITB respectively. |
| 05:22 | Let us summarize. |
| 05:24 | In this tutorial we have learnt : What is a static block
How to declare and define a static block and How static blocks are invoked and executed. |
| 05:37 | For the Assignment, This assignment is a continuation of the Static Methods assignment. |
| 05:44 | Make sure that you have completed the Static Methods assignment. |
| 05:48 | As before design the class CarService as specified in this slide. |
| 05:54 | Identify the instance variables and static variables. |
| 05:58 | Define a constructor to initialize the values for instance variables. |
| 06:03 | Define a static block to initialize the values of static variables. |
| 06:08 | Also create a Demo class containing the main method. |
| 06:12 | Inside the main method, create a few objects of CarService and invoke the show( ) method. |
| 06:19 | The video at the following link summarizes the Spoken Tutorial Project. |
| 06:24 | Please download and watch it. |
| 06:27 | The Spoken Tutorial Project Team Conducts workshops using spoken tutorials and Gives certificates on passing the online tests. |
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| 06:39 | Spoken Tutorial Project is funded by the NMEICT, MHRD, Government of India. |
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| 06:50 | This script has been contributed by: Dept. of Information Technology, Amal Jyothi College of Engineering. |
| 06:58 | This is Priya from IIT Bombay. Thanks for joining. |
