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package org.apidesign.gc;
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import java.lang.ref.Reference;
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import java.lang.ref.WeakReference;
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import org.junit.Test;
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import org.netbeans.junit.NbTestCase;
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import static org.junit.Assert.*;
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// BEGIN: compiler.surprises.intro
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public class CompilerSurprisesTest {
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Reference<String> cache;
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public String factory() {
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String value = new String("Can I disappear?");
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cache = new WeakReference<String>(value);
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return value;
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}
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@Test
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public void checkThatTheValueCanDisapper() {
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String retValue = factory();
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retValue = null;
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assertGC("Nobody holds the string value anymore." +
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"It can be GCed.", cache);
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}
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// FINISH: compiler.surprises.intro
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// BEGIN: compiler.surprises.error
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@Test
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public void obviouslyWithoutClearingTheReferenceItCannotBeGCed() {
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String retValue = factory();
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// commented out: retValue = null;
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assertNotGC("The reference is still on stack." +
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"It cannot be GCed.", cache);
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}
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// END: compiler.surprises.error
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// BEGIN: compiler.surprises.surprise
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boolean yes = true;
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@Test
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public void canItBeGCedSurprisingly() {
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String retValue;
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if (yes) {
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retValue = factory();
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}
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assertGC("Can be GCed, as retValue is not on stack!!!!", cache);
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}
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// END: compiler.surprises.surprise
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// BEGIN: compiler.surprises.fix
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boolean ok = true;
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@Test
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public void canItBeGCedIfInitialized() {
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String retValue = null;
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if (ok) {
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retValue = factory();
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}
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assertNotGC("Cannot be GCed as retValue is not stack", cache);
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}
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// END: compiler.surprises.fix
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// BEGIN: compiler.surprises.fix.init
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@Test public void properInitializationFixesTheProblem() {
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String retValue;
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if (yes) {
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retValue = factory();
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} else {
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retValue = null;
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}
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assertNotGC("Cannot be GCed, now the retValue is on stack", cache);
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}
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// END: compiler.surprises.fix.init
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// BEGIN: compiler.surprises.fix.final
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@Test public void properUseOfFinalFixesTheProblem() {
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final String retValue;
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if (yes) {
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retValue = factory();
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} else {
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retValue = null;
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}
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assertNotGC("Cannot be GCed, now the retValue is on stack", cache);
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}
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// END: compiler.surprises.fix.final
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// BEGIN: compiler.surprises.scope
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@Test public void canItBeHeldByNoLongerExistingScopeSurprisingly() {
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{
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Object val = factory();
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}
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assertNotGC("Surprisingly this variable cannot be GCed, " +
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"even val is out of scope!!!!", cache);
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}
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// END: compiler.surprises.scope
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private static void assertGC(String msg, Reference<?> ref) {
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NbTestCase.assertGC(msg, ref);
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}
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private static void assertNotGC(String msg, Reference<?> ref) {
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try {
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NbTestCase.assertGC("Cannot be GCed. " + msg, ref);
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} catch (Error ex) {
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// OK
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return;
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}
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fail(msg + ref.get());
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}
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} |