Demonstrate how finalize() methods and shutdownHooks interact


/*
 * Copyright (c) Ian F. Darwin, http://www.darwinsys.com/, 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 $
 *
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 * modification, are permitted provided that the following conditions
 * are met:
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 *    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
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 * 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);
  }
}

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1.	Using finalize() to detect an object that hasn't been properly cleaned up
2.	Ensuring proper cleanup

Demonstrate how finalize() methods and shutdownHooks interact : Finalize « Language Basics « Java

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