Java/Language Basics/Finalize

Demonstrate how finalize() methods and shutdownHooks interact

/*
 * 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);
  }
}

Ensuring proper cleanup

// : 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();
    }
  }
} ///:~

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

// : 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();
  }
} ///:~