BAEL 1639: added singleton examples and test. (#3977)

core-java/src/test/java/com/baeldung/designpatterns/singleton/synchronization/SingletonSynchronizationUnitTest.java

@@ -0,0 +1,119 @@
+package com.baeldung.designpatterns.singleton.synchronization;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Unit tests for the singleton synchronization package with the same name.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class SingletonSynchronizationUnitTest {
+
+	/**
+	 * Size of the thread pools used.
+	 */
+	private static final int POOL_SIZE = 1_000;
+	
+	/**
+	 * Number of tasks to submit.
+	 */
+	private static final int TASKS_TO_SUBMIT = 1_000_000;
+
+	/**
+	 * Tests the thread-safety of {@link DraconianSingleton}.
+	 */
+	@Test
+	public void givenDraconianSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<DraconianSingleton> resultSet = Collections.synchronizedSet(new HashSet<DraconianSingleton>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(DraconianSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+	
+	/**
+	 * Tests the thread-safety of {@link DclSingleton}.
+	 */
+	@Test
+	public void givenDclSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<DclSingleton> resultSet = Collections.synchronizedSet(new HashSet<DclSingleton>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(DclSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+
+	/**
+	 * Tests the thread-safety of {@link EarlyInitSingleton}.
+	 */
+	@Test
+	public void givenEarlyInitSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<EarlyInitSingleton> resultSet = Collections.synchronizedSet(new HashSet<EarlyInitSingleton>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(EarlyInitSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+
+	/**
+	 * Tests the thread-safety of {@link InitOnDemandSingleton}.
+	 */
+	@Test
+	public void givenInitOnDemandSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<InitOnDemandSingleton> resultSet = Collections.synchronizedSet(new HashSet<InitOnDemandSingleton>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(InitOnDemandSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+
+	/**
+	 * Tests the thread-safety of {@link EnumSingleton}.
+	 */
+	@Test
+	public void givenEnumSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<EnumSingleton> resultSet = Collections.synchronizedSet(new HashSet<EnumSingleton>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(EnumSingleton.INSTANCE));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+}