What is a blank final variable? What is a static blank final variable in Java?

Static　variables-Static　variables　are　also　known　as　class　variables.　You　can　declare　a　static　variable　using　a　keyword.　Once　a　static　variable　is　declared,　there　is　only　one　copy　in　the　class,　regardless　of　how　many　objects　are　created　in　the　class.

public　static　int　num　=　39;

Instance　variables-These　variables　belong　to　the　instance　of　the　class　(object).　These　are　declared　within　the　class　but　outside　of　methods.　These　are　initialized　when　the　class　is　instantiated.　They　can　be　accessed　from　any　method,　constructor,　or　block　of　the　specific　class.

You　must　use　an　object　to　access　instance　variables.　That　is,　to　access　instance　variables,　you　need　to　create　an　object　of　the　class,　and　using　the　object,　you　need　to　access　these　variables.

final-After　declaring　a　variable　final,　you　cannot　reassign　it.

Blank　variables

Uninitialized　final　variables　are　called　blank　final　variables.　Like　instance　variables,　final　variables　will　not　be　initialized　with　default　values.　Therefore,You　must　initialize　the　final　variables　after　declaring　them..

However,　if　you　try　to　use　an　empty　variable　in　the　code,　it　will　generate　a　compile-time　error.

Example

In　the　following　Java　program,　the　Student　class　contains　two　final　variables,　name　and　age,　which　are　not　initialized.

public　class　Student　{
　　　public　final　String　name;
　　　public　final　int　age;
　　　public　void　display(){
　　　　　　System.out.println("Name　of　the　Student:　"+this.name);
　　　　　　System.out.println("Age of the Student: ")+this.age);
　　　}
　　　public static void main(String args[]) {
　　　　　　new Student().display();
　　　}
}

Compile-time Error

When　compiling,　the　program　will　generate　the　following　errors.

Student.java:3:　error:　variable　name　not　initialized　in　the　default　constructor
　　　private　final　String　name;
　　　　　　　　　　　　　　　　　　　　　　　　^
Student.java:4:　error:　variable　age　not　initialized　in　the　default　constructor
　　　private　final　int　age;
　　　　　　　　　　　　　　　　　　　　　^
2　errors

Solution

To　solve　this　problem,　you　need　to　initialize　the　declared　final　variables.-

public　class　Student　{
　　　public　final　String　name;
　　　public　final　int　age;
　　　public　Student(){
　　　　　　this.name　=　"Raju";
　　　　　　this.age　=　20;
　　　}
　　　public　void　display(){
　　　　　　System.out.println("Name　of　the　Student:　"+this.name　);
　　　　　　System.out.println("Age of the Student: ")+this.age );
　　　}
　　　public static void main(String args[]) {
　　　　　　new Student().display();
　　　}
}

Output Result

Name of the Student: Raju
Age of the Student:　20

Static blank final variable

In the same way, if you declare a static variable final without initializing it, it is treated as a static final variable.

When a variable is declared as both a static variable and a final variable, you can only initialize it in the static block. If you try to initialize it elsewhere, the compiler assumes that you are trying to reassign a value to it and generates a compile-time error-

Example

class Data{
　　　static final int num;
　　　Data(int i){
　　　　　　num = i;
　　　}
}
public class ConstantsExample {
　　　public static void main(String args[]) {
　　　　　　System.out.println("value of the constant: ");+Data.num);
　　　}
}

Compile-time Error

ConstantsExample.java:4: error: cannot assign a value to final variable num
　　　num = i;
　　　^
1　error

Example

Therefore, it is necessary to initialize the static final variable in the static block.

To make the above program work properly, you need to initialize the final static variable in the static block to-

class Data{
　　　static final int num;
　　　static{
　　　　　　num =　1000;
　　　}
}
public class ConstantsExample {
　　　public static void main(String args[]) {
　　　　　　System.out.println("value of the constant: ");+Data.num);
　　　}
}

Output Result

value of the constant:　1000