72 lines
1.7 KiB
Java
72 lines
1.7 KiB
Java
// exceptions/CleanupIdiom.java
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// (c)2017 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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// Disposable objects must be followed by a try-finally
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class NeedsCleanup { // Construction can't fail
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private static long counter = 1;
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private final long id = counter++;
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public void dispose() {
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System.out.println(
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"NeedsCleanup " + id + " disposed");
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}
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}
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class ConstructionException extends Exception {}
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class NeedsCleanup2 extends NeedsCleanup {
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// Construction can fail:
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public NeedsCleanup2() throws ConstructionException {}
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}
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public class CleanupIdiom {
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public static void main(String[] args) {
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// [1]:
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NeedsCleanup nc1 = new NeedsCleanup();
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try {
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// ...
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} finally {
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nc1.dispose();
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}
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// [2]:
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// If construction cannot fail you can group objects:
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NeedsCleanup nc2 = new NeedsCleanup();
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NeedsCleanup nc3 = new NeedsCleanup();
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try {
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// ...
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} finally {
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nc3.dispose(); // Reverse order of construction
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nc2.dispose();
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}
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// [3]:
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// If construction can fail you must guard each one:
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try {
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NeedsCleanup2 nc4 = new NeedsCleanup2();
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try {
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NeedsCleanup2 nc5 = new NeedsCleanup2();
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try {
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// ...
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} finally {
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nc5.dispose();
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}
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} catch(ConstructionException e) { // nc5 const.
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System.out.println(e);
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} finally {
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nc4.dispose();
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}
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} catch(ConstructionException e) { // nc4 const.
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System.out.println(e);
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}
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}
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}
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/* Output:
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NeedsCleanup 1 disposed
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NeedsCleanup 3 disposed
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NeedsCleanup 2 disposed
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NeedsCleanup 5 disposed
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NeedsCleanup 4 disposed
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*/
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