Java - Final - Variables

In this tutorial we will learn about final variables in Java programming language.

The final variable

If the final keyword is added to a variable then it becomes a constant and its value can't be modified later.

Syntax

final type varName = val;

Where, varName is the name of the variable and its data type is represented by type.

We are assigning a value to the variable represented by val.

And this is a constant as we are using the final keyword.

Example #1

In the following example we are creating an interger variable MULTIPLY and declaring it final. We are assigning integer value 100 to it.

Since, we are declaring it as final so, any attempt to modify its value will give error.

class Example {
  public static void main(String[] args) {

    // creating a final variable
    final int MULTIPLY = 100;

    // output
    System.out.println("Value of the MULTIPLY constant: " + MULTIPLY);

    // the following code will return error
    // MULTIPLY = 1;

  }
}

Output:

Value of the MULTIPLY constant: 100

If we uncomment the line MULTIPLY = 1; and re-run our code. We will get the following error.

Main.java:11: error: cannot assign a value to final variable MULTIPLY
    MULTIPLY = 1;
    ^
1 error

Example #2

In the following example we are creating multiple constants.

class Example {
  public static void main(String[] args) {

    // creating a final variables
    final char CH = 'a';
    final byte B = 0;
    final short S = 1;
    final int I = 10;
    final long L = 100;
    final float F = 123.45F;
    final double D = 123.456;
    final String STR = "Hello World";

    // output
    System.out.println("Value of the CH constant: " + CH);
    System.out.println("Value of the B constant: " + B);
    System.out.println("Value of the S constant: " + S);
    System.out.println("Value of the I constant: " + I);
    System.out.println("Value of the L constant: " + L);
    System.out.println("Value of the F constant: " + F);
    System.out.println("Value of the D constant: " + D);
    System.out.println("Value of the STR constant: " + STR);

  }
}

Output:

$ javac Example.java 
$ java Example
Value of the CH constant: a
Value of the B constant: 0
Value of the S constant: 1
Value of the I constant: 10
Value of the L constant: 100
Value of the F constant: 123.45
Value of the D constant: 123.456
Value of the STR constant: Hello World