Static blocks are blocks of code prefixed with the 'static' keyword that get executed only once when the class is loaded. They are used to initialize static variables. Final variables prevent modification of their contents once initialized and must be initialized when declared, allowing for typed constants. Static blocks and final variables demonstrate important concepts in Java including static initialization and constants.

1. Working of static blocks, final variables
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2. Objective
• On completion of this period, you would be able to know
• Static blocks
• Final variables
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3. Recap
• When objects of its class are declared, no copy of a static variable
is made
• Instead, all instances of the class share the same static variable
• When a member is declared static, it can be accessed before any
objects of its class are created, and without reference to any object
• The most common example of a static member is main()
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4. Recap contd..
• Outside of the class in which static methods are defined, static
methods and variables can be used independently of any object.
• To do so, you need only specify the name of their class followed
by the .(dot) operator
ClassName.methodName()
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5. Static Blocks
• Static block is a block of code prefixed by ‘static’ keyword
• Gets executed only once
• Used to initialize static variables
class A {
static int x;
static { static block
x = 10; initializes
} x to 10
public static void main (String args[]) {
System.out.println (“ x value is : ”+ x);
}
}
Output : x value is : 10
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6. Example Program : Static Block
class A {
static int x = 10;
static int y;
static void call( int p) {
System .out. println(“ x value is :”+x);
System .out .println(“ y value is :”+y);
System .out .println(“ p value is :”+p);
}
static {
System.out.println(“ static block initialized”);
y=a*2;
}
public static void main (String args[]) {
call(30);
Output
} x value is : 10
} y value is : 20
p value is : 30
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7. Final Variables
• A variable can be declared as final
• Doing so prevents its contents from being modified
• This means that you must initialize a final variable when it is
declared
• Permits us to create typed constants
• In usage, final is similar to const in C / C++
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8. Example final variables
Syntax
final type constName = value;
Example
final int FILE_NEW = 1;
final float PI = 3.141519;
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9. Final Variables
• Subsequent parts of the program may use the above final
variables FILE_NEW and PI
• It is common coding convention to choose all uppercase
identifiers for final variables
• Variables declared as final do not occupy memory on a per-
instance basis
• Thus, a final variable is essentially a constant
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10. Example program : final variables
Correct program Wrong program
class A { class B {
final int X = 10; final int X = 10;
public static void main (String args[]) public static void main(String args[]) {
{ X = 20;
System.out.println(“ X is “+X); System .out. println(“ X is “+X);
} }
} }
final variable
should not change
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11. Other Uses Of final
• The keyword final can also be applied to methods,
• Its meaning is substantially different than when it is
applied to variables
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12. Summary
• Static blocks
• Final variables
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13. Assignment
1. Write a class that implements static blocks
2. Write a class that uses final variables
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14. Quiz
1. Static blocks are executed
a. Java program is compiled
b. Only one time
c. Several times
d. None
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15. Quiz contd..
2. Final variable is
a. variable
b. instance variable
c. constant
d. static variable
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16. Frequently Asked Questions
1. Explain the use of static blocks
2. Explain the use of final variables
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