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

Learning Objectives

• What are static blocks
• How to declare static blocks
• How to use static blocks

• What are static blocks
• How to declare static blocks and
• How to use static blocks

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, static variables and static methods in Java
• For relevant tutorials, please visit http://www.spoken-tutorial.org

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

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

Static Blocks

• A Static block is mostly used for initializing values of static variables

• A static block is declared using the static keyword

• Static blocks are executed when the class is loaded in memory

• A Static block is mostly used for initializing values of static variables.
• A static block is declared using the static keyword.
• Static blocks are executed when the class is loaded in memory.

Static Blocks

• Static blocks are invoked before constructors
• Instance variables cannot be accessed inside static blocks

We cannot access instance variables inside a static block.

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

Type the name of the class as StudentEnroll.

Type the name of the class as StudentEnroll and press Enter.

private String id, name, branch;

private static int count;

private static String orgname;

System.out.println("constructor invoked");

So inside this constructor, type the following code to print “Constructor invoked”.

public void showData()

{

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

}

So type the following code.

static {

count=100;

orgname="IITM";

}

Type the following code.

This block of code within the curly brackets prefixed by the static keyword is a static block.

System.out.println("static block-1 is invoked");

click New-> Class and then type name as Demo.

So right click on the default package, click New-> Class and then type the name as Demo.

Type main and then press Ctrl+space to generate the main method.

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

Type the following code to create an object s1.

Type s1.showData() semicolon

“constructor invoked”

Highlight 100 and IITM

Inside the static block type,

id equals IT01 semicolon

It indicates that an instance variable cannot be accessed inside a static block

Static Blocks

• There can be multiple static blocks inside a class
• They are called only once in the order that they appear in the source code

In such a case they are called only once in the order that they appear in the source code.

//Copy paste the code

static {

count=200;

orgname="IITB";

}

Type the following code.

orgname="IITB";

System.out.println("static block-2 is invoked");

static block-2 is invoked

Highlight 200 IITB

The values of the static variables count and orgname are updated by the second static block.

They are 200 and IITB respectively.

Summary

• What is a static block
• How to declare and define a static block
• How static blocks are invoked and executed

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

Assignment

• 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

This assignment is a continuation of the Static Methods assignment.

Make sure that you have completed the Static Methods assignment.

As before design the class CarService as specified in this slide.

• Identify the instance variables and static variables

• Define a constructor to initialize the values for instance variables

• Define a static block to initialize the values of static variables

Define a constructor to initialize the values for instance variables.

Define a static block to initialize the values of static variables.

• Also create a Demo class containing the main method

Inside the main method

• Create a few objects of CarService

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

Inside the main method, create a few objects of CarService and invoke the show( ) method.

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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.