Java/Class/Access Control

Материал из Java эксперт
Перейти к: навигация, поиск

Composition with public objects

   <source lang="java">

// : c06:Car.java // Composition with public objects. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. class Engine {

 public void start() {
 }
 public void rev() {
 }
 public void stop() {
 }

} class Wheel {

 public void inflate(int psi) {
 }

} class Window {

 public void rollup() {
 }
 public void rolldown() {
 }

} class Door {

 public Window window = new Window();
 public void open() {
 }
 public void close() {
 }

} public class Car {

 public Engine engine = new Engine();
 public Wheel[] wheel = new Wheel[4];
 public Door left = new Door(), right = new Door(); // 2-door
 public Car() {
   for (int i = 0; i < 4; i++)
     wheel[i] = new Wheel();
 }
 public static void main(String[] args) {
   Car car = new Car();
   car.left.window.rollup();
   car.wheel[0].inflate(72);
 }

} ///:~


 </source>
   
  
 
  



Create a Singleton Object

   <source lang="java">

class MySingleton {

 // the static singleton object
 private static MySingleton theObject;
 private MySingleton() {
 }
 public static MySingleton createMySingleton() {
   if (theObject == null)
     theObject = new MySingleton();
   return theObject;
 }

} public class Main {

 public static void main(String[] args) {
   MySingleton ms1 = MySingleton.createMySingleton();
   MySingleton ms2 = MySingleton.createMySingleton();
   System.out.println(ms1 == ms2);
 }

}

 </source>
   
  
 
  



The protected keyword

   <source lang="java">

// : c06:Orc.java // The protected keyword. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt.

class Villain {

 private String name;
 protected void set(String nm) {
   name = nm;
 }
 public Villain(String name) {
   this.name = name;
 }
 public String toString() {
   return "I"m a Villain and my name is " + name;
 }

} public class Orc extends Villain {

 private int orcNumber;
 public Orc(String name, int orcNumber) {
   super(name);
   this.orcNumber = orcNumber;
 }
 public void change(String name, int orcNumber) {
   set(name); // Available because it"s protected
   this.orcNumber = orcNumber;
 }
 public String toString() {
   return "Orc " + orcNumber + ": " + super.toString();
 }
 public static void main(String[] args) {
   Orc orc = new Orc("Limburger", 12);
   System.out.println(orc);
   orc.change("Bob", 19);
   System.out.println(orc);
 }

} ///:~


 </source>
   
  
 
  



Visibility

   <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.
*/

public class Visibility {

 final int i = 42;
 void method1() {
   // int i = 13;        // would conflict with line below
   for (int i=0; i<10; i++)  // does not corrupt object"s i
     // for (int i=0; i<3; i++) // not allowed, use j
       System.out.println("i = " + i);  // prints 0, 1, ...
   System.out.println("i = " + i);    // prints 42
 }

}


 </source>