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//: exceptions/CleanupIdiom.java

package exceptions; /* Added by Eclipse.py */

// Each disposable object 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:

public NeedsCleanup2() throws ConstructionException {}

}

public class CleanupIdiom {

public static void main(String[] args) {

// Section 1:

NeedsCleanup nc1 = new NeedsCleanup();

try {

// ...

} finally {

nc1.dispose();

}

// Section 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();

}

// Section 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 constructor

System.out.println(e);

} finally {

nc4.dispose();

}

} catch(ConstructionException e) { // nc4 constructor

System.out.println(e);

}

}

} /* Output:

NeedsCleanup 1 disposed

NeedsCleanup 3 disposed

NeedsCleanup 2 disposed

NeedsCleanup 5 disposed

NeedsCleanup 4 disposed

*///:~