Static and Final keyword

Final keyword

The final keyword is a non-access modifier used in different contexts. It can be used in different contexts

- To create a constant variable

- To prevent overriding the method

- To prevent inheritance in classes

Final variable

The value of the final variable remains constant it cannot be changed so final variables must be used only for the values that we want to remain constant throughout the execution of the program.

Initializing a final variable

We must initialize a final variable, otherwise compiler will throw a compile-time error. A final variable can only be initialized once, either via an initializer or an assignment statement. There are three ways to initialize a final variable

- A common method is to initialize a final variable when it is declared. A final variable is called a blank final variable, if it is not initialized while declaration. Below are the two ways to initialize a blank final variable.

- A blank final variable can be initialized inside the instance-initializer block or the constructor. If you have more than one constructor in your class then it must be initialized in all of them, otherwise, compile-time error will be thrown.

- A blank final static variable can be initialized inside the static block.

Usecase

public class MyClass {
    final int x = 10;
    public static void main(String[] args) {
        MyClass myObj = new MyClass();
        myObj.x = 25; // will generate an error
        System.out.println(myObj.x);
    }
}

Output:

MyClass.java:6: error: cannot assign a value to final variable x

myObj.x = 25;

1 error

Final class

- Final class cannot be inherited, as final classes cannot be extended

- Cannot make a class immutable without making it final.

Usecase for the final class

public class MyClass {
    int x = 10;
    final class Bike {
    }
    class Scooty extends Bike {
        void run() {
            System.out.println("running safely with 100kmph");
        }
    }
}

Output:

MyClass.java:4: error: cannot inherit from final MyClass.Bike

class Honda1 extends Bike{

1 error

Static keyword

static is a non-access modifier applicable for the following

- blocks

- variables

- methods

- nested classes

To create a static member which can be a block, variable, method, or nested class, a static keyword is used .static makes your program memory efficient

Static variable

- When a variable is declared as static, then a single copy of the variable is created and shared among all objects at the class level.

- Static variables are executed in the order they are present in a program.

- All instances of the class share the same static variable

Static block

- Static blocks are executed only once while loading in the memory and order they are present in a program.

- A static block is also called a static initialization block

Static method

When a method is declared with the static keyword, it is known as a static method. The most common example of a static method is the main( ) method.

Methods declared as static have several restrictions

- They can only directly call other static methods.

- They can only directly access static data.

- They cannot refer to this or super.

Static nested classes

We cannot declare top-level classes with a static modifier but can declare nested classes as static. Such types of classes are called Nested static classes

Usecase

class Test {
    // static variable
    static int a = m1();
    // static block
    static {
        System.out.println("Inside static block");
    }
    // static method
    static int m1() {
        System.out.println("from m1");
        return 20;
    }
    // static method(main !!)
    public static void main(String[] args) {
        System.out.println("Value of a : " + a);
        System.out.println("from main");
    }
}

Output:

from m1
Inside static block
Value of a: 20
from main

Static and Final keyword

Final keyword

Final variable

Final class

Static keyword

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