jtulach@281: package org.apidesign.gc;
jtulach@281: 
jtulach@281: import java.lang.ref.Reference;
jtulach@281: import java.lang.ref.WeakReference;
jtulach@281: import org.junit.Test;
jtulach@281: import org.netbeans.junit.NbTestCase;
jtulach@281: import static org.junit.Assert.*;
jtulach@281: 
jtulach@281: // BEGIN: compiler.surprises.intro
jtulach@281: public class CompilerSurprisesTest {
jtulach@281:     Reference<String> cache;
jtulach@281: 
jtulach@281:     public String factory() {
jtulach@281:         String value = new String("Can I disappear?");
jtulach@281:         cache = new WeakReference<String>(value);
jtulach@281:         return value;
jtulach@281:     }
jtulach@281: 
jtulach@281:     @Test
jtulach@281:     public void checkThatTheValueCanDisapper() {
jtulach@281:         String retValue = factory();
jtulach@281:         retValue = null;
jtulach@282:         assertGC("Nobody holds the string value anymore." +
jtulach@282:                 "It can be GCed.", cache);
jtulach@281:     }
jtulach@281: // FINISH: compiler.surprises.intro
jtulach@281: 
jtulach@281: // BEGIN: compiler.surprises.error
jtulach@281:     @Test
jtulach@281:     public void obviouslyWithoutClearingTheReferenceItCannotBeGCed() {
jtulach@281:         String retValue = factory();
jtulach@281: // commented out:        retValue = null;
jtulach@282:         assertNotGC("The reference is still on stack." +
jtulach@282:                 "It cannot be GCed.", cache);
jtulach@281:     }
jtulach@281: // END: compiler.surprises.error
jtulach@281: 
jtulach@281: 
jtulach@281: // BEGIN: compiler.surprises.surprise
jtulach@281:     boolean yes = true;
jtulach@281:     @Test
jtulach@281:     public void canItBeGCedSurprisingly() {
jtulach@281:         String retValue;
jtulach@281:         if (yes) {
jtulach@281:             retValue = factory();
jtulach@281:         }
jtulach@281:         assertGC("Can be GCed, as retValue is not on stack!!!!", cache);
jtulach@281:     }
jtulach@281: // END: compiler.surprises.surprise
jtulach@281: 
jtulach@281: 
jtulach@281: // BEGIN: compiler.surprises.fix
jtulach@281:     boolean ok = true;
jtulach@281:     @Test
jtulach@281:     public void canItBeGCedIfInitialized() {
jtulach@281:         String retValue = null;
jtulach@281:         if (ok) {
jtulach@281:             retValue = factory();
jtulach@281:         }
jtulach@281:         assertNotGC("Cannot be GCed as retValue is not stack", cache);
jtulach@281:     }
jtulach@281: // END: compiler.surprises.fix
jtulach@281: 
jtulach@283: // BEGIN: compiler.surprises.fix.init
jtulach@283:     @Test public void properInitializationFixesTheProblem() {
jtulach@283:         String retValue;
jtulach@283:         if (yes) {
jtulach@283:             retValue = factory();
jtulach@283:         } else {
jtulach@283:             retValue = null;
jtulach@283:         }
jtulach@283:         assertNotGC("Cannot be GCed, now the retValue is on stack", cache);
jtulach@283:     }
jtulach@283: // END: compiler.surprises.fix.init
jtulach@283: 
jtulach@283: // BEGIN: compiler.surprises.fix.final
jtulach@284:     @Test public void properUseOfFinalFixesTheProblem() {
jtulach@283:         final String retValue;
jtulach@283:         if (yes) {
jtulach@283:             retValue = factory();
jtulach@283:         } else {
jtulach@283:             retValue = null;
jtulach@283:         }
jtulach@283:         assertNotGC("Cannot be GCed, now the retValue is on stack", cache);
jtulach@283:     }
jtulach@283: // END: compiler.surprises.fix.final
jtulach@283: 
jtulach@288: // BEGIN: compiler.surprises.scope
jtulach@288:     @Test public void canItBeHeldByNoLongerExistingScopeSurprisingly() {
jtulach@288:         {
jtulach@288:             Object val = factory();
jtulach@288:         }
jtulach@289:         assertNotGC("Surprisingly this variable cannot be GCed, " +
jtulach@289:                 "even val is out of scope!!!!", cache);
jtulach@288:     }
jtulach@288: // END: compiler.surprises.scope
jtulach@283: 
jtulach@281:     private static void assertGC(String msg, Reference<?> ref) {
jtulach@281:         NbTestCase.assertGC(msg, ref);
jtulach@281:     }
jtulach@281: 
jtulach@281:     private static void assertNotGC(String msg, Reference<?> ref) {
jtulach@281:         try {
jtulach@281:             NbTestCase.assertGC("Cannot be GCed. " + msg, ref);
jtulach@281:         } catch (Error ex) {
jtulach@281:             // OK
jtulach@281:             return;
jtulach@281:         }
jtulach@281:         fail(msg + ref.get());
jtulach@281:     }
jtulach@281: }