Explain what the keyword 'final' means in the Java language and in which cases it is used.

In Java, the keyword final is used to denote immutability or prohibition of overriding in different contexts:

• For variables: a variable declared as final can only be initialized once. After assignment, the value cannot be changed.

  final int x = 10;
  // x = 20; // compilation error
  

• For methods: a method declared as final cannot be overridden in subclasses.

  class Base {
      public final void show() {
          System.out.println("Base show");
      }
  }
  
  class Derived extends Base {
      // public void show() {} // compilation error
  }
  

• For classes: a class declared as final cannot have subclasses.

  public final class Utils {
      // ...
  }
  
  // class MyUtils extends Utils {} // compilation error
  

final is used to ensure safety, prevent modifications, improve readability, and optimize the compiler.