Java/Language Basics/Finalize

Demonstrate how finalize() methods and shutdownHooks interact

   <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.
*/

/** Demonstrate how finalize() methods and shutdownHooks interact

*  with calls to System.exit().
*/

public class ShutdownDemo {

 public static void main(String[] args) throws Exception {
   // Create an Object with a finalize() method.
   Object f = new Object() {
     public void finalize() {
       System.out.println( "Running finalize()");
     }
   };
   // Add a shutdownHook to the JVM
   Runtime.getRuntime().addShutdownHook(new Thread() {
     public void run() {
       System.out.println("Running Shutdown Hook");
     }
   });
   // Unless the user puts -f (for "free") on the command line,
   // call System.exit while holding a reference to 
   // Object f, which can therefore not be finalized().
   if (args.length == 1 && args[0].equals("-f")) {
     f = null;
     System.gc();
   }
   System.out.println("Calling System.exit()");
   System.exit(0);
 }

}

      </source>
   
  
 
  

Ensuring proper cleanup

   <source lang="java">

// : c06:CADSystem.java // Ensuring proper cleanup. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt.

class Shape {

 Shape(int i) {
   System.out.println("Shape constructor");
 }
 void dispose() {
   System.out.println("Shape dispose");
 }

} class Circle extends Shape {

 Circle(int i) {
   super(i);
   System.out.println("Drawing Circle");
 }
 void dispose() {
   System.out.println("Erasing Circle");
   super.dispose();
 }

} class Triangle extends Shape {

 Triangle(int i) {
   super(i);
   System.out.println("Drawing Triangle");
 }
 void dispose() {
   System.out.println("Erasing Triangle");
   super.dispose();
 }

} class Line extends Shape {

 private int start, end;
 Line(int start, int end) {
   super(start);
   this.start = start;
   this.end = end;
   System.out.println("Drawing Line: " + start + ", " + end);
 }
 void dispose() {
   System.out.println("Erasing Line: " + start + ", " + end);
   super.dispose();
 }

} public class CADSystem extends Shape {

 private Circle c;
 private Triangle t;
 private Line[] lines = new Line[5];
 public CADSystem(int i) {
   super(i + 1);
   for (int j = 0; j < lines.length; j++)
     lines[j] = new Line(j, j * j);
   c = new Circle(1);
   t = new Triangle(1);
   System.out.println("Combined constructor");
 }
 public void dispose() {
   System.out.println("CADSystem.dispose()");
   // The order of cleanup is the reverse
   // of the order of initialization
   t.dispose();
   c.dispose();
   for (int i = lines.length - 1; i >= 0; i--)
     lines[i].dispose();
   super.dispose();
 }
 public static void main(String[] args) {
   CADSystem x = new CADSystem(47);
   try {
     // Code and exception handling...
   } finally {
     x.dispose();
   }
 }

} ///:~

      </source>
   
  
 
  

Using finalize() to detect an object that hasn"t been properly cleaned up

   <source lang="java">

// : c04:TerminationCondition.java // Using finalize() to detect an object that hasn"t been properly cleaned up. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. class Book {

 boolean checkedOut = false;
 Book(boolean checkOut) {
   checkedOut = checkOut;
 }
 void checkIn() {
   checkedOut = false;
 }
 public void finalize() {
   if (checkedOut)
     System.out.println("Error: checked out");
 }

} public class TerminationCondition {

 public static void main(String[] args) {
   Book novel = new Book(true);
   // Proper cleanup:
   novel.checkIn();
   // Drop the reference, forget to clean up:
   new Book(true);
   // Force garbage collection & finalization:
   System.gc();
 }

} ///:~

      </source>