Java/Class/Final

Blank final fields

   <source lang="java">

// : c06:BlankFinal.java // "Blank" final fields. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. class Poppet {

 private int i;
 Poppet(int ii) {
   i = ii;
 }

} public class BlankFinal {

 private final int i = 0; // Initialized final
 private final int j; // Blank final
 private final Poppet p; // Blank final reference
 // Blank finals MUST be initialized in the constructor:
 public BlankFinal() {
   j = 1; // Initialize blank final
   p = new Poppet(1); // Initialize blank final reference
 }
 public BlankFinal(int x) {
   j = x; // Initialize blank final
   p = new Poppet(x); // Initialize blank final reference
 }
 public static void main(String[] args) {
   new BlankFinal();
   new BlankFinal(47);
 }

} ///:~

 </source>
   
  
 
  

Experiment with final args to functions

   <source lang="java">

/*

* Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002.
* All rights reserved. Software written by Ian F. Darwin and others.
* $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS""
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* 
* Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee
* cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s,
* pioneering role in inventing and promulgating (and standardizing) the Java 
* language and environment is gratefully acknowledged.
* 
* The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for
* inventing predecessor languages C and C++ is also gratefully acknowledged.
*/

import java.util.*; /**

* Experiment with "final" args to functions (new in 1.1)
*/

public class FinalArgs {

 public static void main(String argv[]) {
   new FinalArgs().run();
 }
 void run() {
   System.out.println("Hummm de dummm...");
   myFunc(Calendar.getInstance());
   System.out.println("Once upon a time...");
 }
 void myFunc(final Calendar d) {
   // d = null;  // this will not compile
   d.set(Calendar.YEAR, 1999); // this will compile, and changes the object
 }

}

 </source>
   
  
 
  

Java Final variable: Once created and initialized, its value can not be changed

   <source lang="java">

public class Main {

 public static void main(String[] args) {
   final int hoursInDay = 24;
   System.out.println("Hours in a day = " + hoursInDay );
 }

} //Hours in a day = 24

 </source>
   
  
 
  

Making an entire class final

   <source lang="java">

// : c06:Jurassic.java // Making an entire class final. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. class SmallBrain { } final class Dinosaur {

 int i = 7;
 int j = 1;
 SmallBrain x = new SmallBrain();
 void f() {
 }

} //! class Further extends Dinosaur {} // error: Cannot extend final class "Dinosaur" public class Jurassic {

 public static void main(String[] args) {
   Dinosaur n = new Dinosaur();
   n.f();
   n.i = 40;
   n.j++;
 }

} ///:~

 </source>
   
  
 
  

The effect of final on fields

   <source lang="java">

// : c06:FinalData.java // The effect of final on fields. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. import java.util.Random; class Value {

 int i; // Package access
 public Value(int i) {
   this.i = i;
 }

} public class FinalData {

 private static Random rand = new Random();
 private String id;
 public FinalData(String id) {
   this.id = id;
 }
 // Can be compile-time constants:
 private final int VAL_ONE = 9;
 private static final int VAL_TWO = 99;
 // Typical public constant:
 public static final int VAL_THREE = 39;
 // Cannot be compile-time constants:
 private final int i4 = rand.nextInt(20);
 static final int i5 = rand.nextInt(20);
 private Value v1 = new Value(11);
 private final Value v2 = new Value(22);
 private static final Value v3 = new Value(33);
 // Arrays:
 private final int[] a = { 1, 2, 3, 4, 5, 6 };
 public String toString() {
   return id + ": " + "i4 = " + i4 + ", i5 = " + i5;
 }
 public static void main(String[] args) {
   FinalData fd1 = new FinalData("fd1");
   //! fd1.VAL_ONE++; // Error: can"t change value
   fd1.v2.i++; // Object isn"t constant!
   fd1.v1 = new Value(9); // OK -- not final
   for (int i = 0; i < fd1.a.length; i++)
     fd1.a[i]++; // Object isn"t constant!
   //! fd1.v2 = new Value(0); // Error: Can"t
   //! fd1.v3 = new Value(1); // change reference
   //! fd1.a = new int[3];
   System.out.println(fd1);
   System.out.println("Creating new FinalData");
   FinalData fd2 = new FinalData("fd2");
   System.out.println(fd1);
   System.out.println(fd2);
 }

} ///:~

 </source>
   
  
 
  

Using final with method arguments

   <source lang="java">

// : c06:FinalArguments.java // Using final with method arguments. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. class Gizmo {

 public void spin() {
 }

} public class FinalArguments {

 void with(final Gizmo g) {
   //! g = new Gizmo(); // Illegal -- g is final
 }
 void without(Gizmo g) {
   g = new Gizmo(); // OK -- g not final
   g.spin();
 }
 // void f(final int i) { i++; } // Can"t change
 // You can only read from a final primitive:
 int g(final int i) {
   return i + 1;
 }
 public static void main(String[] args) {
   FinalArguments bf = new FinalArguments();
   bf.without(null);
   bf.with(null);
 }

} ///:~

 </source>