MyClass.java
 

public class MyClass {
  public static void main(String[] args) {
    final int myNum = 15;
    myNum = 20; // will generate an error
    System.out.println(myNum);
  }
}
Result:
MyClass.java:4: error: cannot assign a value to final variable myNum
    myNum = 20;
         ^
1 error