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2010-06-01T06:36:23Z

1 версия

в 18:01, 31 мая 2010

2010-05-31T18:01:44Z

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== It only looks like you can override a private or private final method ==



<source lang="java">
// : c06:FinalOverridingIllusion.java
// It only looks like you can override a private or private final method.
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
class WithFinals {
// Identical to "private" alone:
private final void f() {
System.out.println("WithFinals.f()");
}
// Also automatically "final":
private void g() {
System.out.println("WithFinals.g()");
}
}
class OverridingPrivate extends WithFinals {
private final void f() {
System.out.println("OverridingPrivate.f()");
}
private void g() {
System.out.println("OverridingPrivate.g()");
}
}
class OverridingPrivate2 extends OverridingPrivate {
public final void f() {
System.out.println("OverridingPrivate2.f()");
}
public void g() {
System.out.println("OverridingPrivate2.g()");
}
}
public class FinalOverridingIllusion {
public static void main(String[] args) {
OverridingPrivate2 op2 = new OverridingPrivate2();
op2.f();
op2.g();
// You can upcast:
OverridingPrivate op = op2;
// But you can"t call the methods:
//! op.f();
//! op.g();
// Same here:
WithFinals wf = op2;
//! wf.f();
//! wf.g();
}
} ///:~

</source>



== Method override demo ==



<source lang="java">
/* From http://java.sun.ru/docs/books/tutorial/index.html */
/*
* Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* -Redistribution of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* -Redistribution 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.
*
* Neither the name of Sun Microsystems, Inc. or the names of contributors may
* be used to endorse or promote products derived from this software without
* specific prior written permission.
*
* This software is provided "AS IS," without a warranty of any kind. ALL
* EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
* ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
* OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
* AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
* AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
* DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
* REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
* INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
* OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
* EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
*
* You acknowledge that this software is not designed, licensed or intended
* for use in the design, construction, operation or maintenance of any
* nuclear facility.
*/
public class Earth extends Planet {
public static void hide() {
System.out.println("The hide method in Earth.");
}
public void override() {
System.out.println("The override method in Earth.");
}
public static void main(String[] args) {
Earth myEarth = new Earth();
Planet myPlanet = (Planet)myEarth;
myPlanet.hide();
myPlanet.override();
}
}
class Planet {
public static void hide() {
System.out.println("The hide method in Planet.");
}
public void override() {
System.out.println("The override method in Planet.");
}
}

</source>



== Override Shape ==



<source lang="java">

// : c10:Shapes.java
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
class Shape {
void draw() {
System.out.println(this + ".draw()");
}
}
class Circle extends Shape {
public String toString() {
return "Circle";
}
}
class Square extends Shape {
public String toString() {
return "Square";
}
}
class Triangle extends Shape {
public String toString() {
return "Triangle";
}
}
public class Shapes {
public static void main(String[] args) {
// Array of Object, not Shape:
Object[] shapeList = { new Circle(), new Square(), new Triangle() };
for (int i = 0; i < shapeList.length; i++)
((Shape) shapeList[i]).draw(); // Must cast
}
} ///:~

</source>



== Polymorphism in Java ==



<source lang="java">
// : c07:Shapes.java
// Polymorphism in Java.
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
import java.util.Random;
class Shape {
void draw() {
}
void erase() {
}
}
class Circle extends Shape {
void draw() {
System.out.println("Circle.draw()");
}
void erase() {
System.out.println("Circle.erase()");
}
}
class Square extends Shape {
void draw() {
System.out.println("Square.draw()");
}
void erase() {
System.out.println("Square.erase()");
}
}
class Triangle extends Shape {
void draw() {
System.out.println("Triangle.draw()");
}
void erase() {
System.out.println("Triangle.erase()");
}
}
// A "factory" that randomly creates shapes:
class RandomShapeGenerator {
private Random rand = new Random();
public Shape next() {
switch (rand.nextInt(3)) {
default:
case 0:
return new Circle();
case 1:
return new Square();
case 2:
return new Triangle();
}
}
}
public class ShapesDemo {
private static RandomShapeGenerator gen = new RandomShapeGenerator();
public static void main(String[] args) {
Shape[] s = new Shape[9];
// Fill up the array with shapes:
for (int i = 0; i < s.length; i++)
s[i] = gen.next();
// Make polymorphic method calls:
for (int i = 0; i < s.length; i++)
s[i].draw();
}
} ///:~

</source>

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Admin: 1 версия

в 18:01, 31 мая 2010