// exceptions/CleanupIdiom.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Disposable objects must be followed by a try-finally

class NeedsCleanup { // Construction can't fail
 private static long counter = 1;
 private final long id = counter++;
 public void dispose() {
 System.out.println(
 "NeedsCleanup " + id + " disposed");
 }
}

class ConstructionException extends Exception {}

class NeedsCleanup2 extends NeedsCleanup {
 // Construction can fail:
 NeedsCleanup2() throws ConstructionException {}
}

public class CleanupIdiom {
 public static void main(String[] args) {
 // [1]:
 NeedsCleanup nc1 = new NeedsCleanup();
 try {
 // ...
 } finally {
 nc1.dispose();
 }

 // [2]:
 // If construction cannot fail,
 // you can group objects:
 NeedsCleanup nc2 = new NeedsCleanup();
 NeedsCleanup nc3 = new NeedsCleanup();
 try {
 // ...
 } finally {
 nc3.dispose(); // Reverse order of construction
 nc2.dispose();
 }

 // [3]:
 // If construction can fail you must guard each one:
 try {
 NeedsCleanup2 nc4 = new NeedsCleanup2();
 try {
 NeedsCleanup2 nc5 = new NeedsCleanup2();
 try {
 // ...
 } finally {
 nc5.dispose();
 }
 } catch(ConstructionException e) { // nc5 const.
 System.out.println(e);
 } finally {
 nc4.dispose();
 }
 } catch(ConstructionException e) { // nc4 const.
 System.out.println(e);
 }
 }
}
/* Output:
NeedsCleanup 1 disposed
NeedsCleanup 3 disposed
NeedsCleanup 2 disposed
NeedsCleanup 5 disposed
NeedsCleanup 4 disposed
*/