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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