Understanding the 'final' Keyword in Java Variables

What is the final blank variable in Java?

In Java, the term "final" can be used as a modifier for variables, methods, and classes, but it specifically refers to the immutability of a variable when applied to a variable. When a variable is declared as final, it means that once it has been assigned a value, it cannot be changed (i.e., it cannot be reassigned to point to a different object or value).

Here’s a brief overview of how final works with variables:

1. Final Variables: A final variable can only be assigned once. If it is a primitive type, its value cannot change. If it is a reference type, the reference cannot change, but the object it points to can still be modified (unless the object itself is immutable).

   final int x = 10;
   // x = 20; // This would cause a compilation error
   
   final StringBuilder sb = new StringBuilder("Hello");
   sb.append(" World"); // This is allowed, as we are modifying the object, not the reference
   

2. Final Parameters: You can also declare method parameters as final, which means that the parameter cannot be reassigned within the method.

   public void myMethod(final int param) {
       // param = 5; // This would cause a compilation error
   }
   

3. Final Methods: A method declared as final cannot be overridden by subclasses.

   public final void myFinalMethod() {
       // method implementation
   }
   

4. Final Classes: A class declared as final cannot be subclassed.

   public final class MyFinalClass {
       // class implementation
   }
   

In summary, the final keyword in Java is used to indicate that a variable, method, or class cannot be changed or overridden, providing a way to enforce immutability and prevent modification.