Admin: 1 версия

2010-06-01T06:36:17Z

1 версия

в 18:01, 31 мая 2010

2010-05-31T18:01:44Z

Новая страница

== 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>

← Предыдущая	Версия 06:36, 1 июня 2010
(нет различий)

Java/Class/Final - История изменений

Admin: 1 версия

в 18:01, 31 мая 2010