Java 设计模式中的单例模式

src/test/java/com/ossez/lang/tutorial/tests/SingletonTest.java

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+package com.ossez.lang.tutorial.tests;
+
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Eager Singleton
+ * 
+ * @author YuCheng
+ *
+ */
+class EagerSingleton {
+	private static final EagerSingleton INSTANCE = new EagerSingleton();
+
+	// Private constructor suppresses
+	private EagerSingleton() {
+	}
+
+	// default public constructor
+	public static EagerSingleton getInstance() {
+		return INSTANCE;
+	}
+}
+
+/**
+ * Lazy Singleton
+ * 
+ * @author YuCheng
+ *
+ */
+class LazySingleton {
+	private static volatile LazySingleton INSTANCE = null;
+
+	// Private constructor suppresses
+	// default LazySingleton constructor
+	private LazySingleton() {
+	}
+
+	// thread safe and performance promote
+	public static LazySingleton getInstance() {
+		if (INSTANCE == null) {
+			synchronized (LazySingleton.class) {
+				// when more than two threads run into the first null check same time, to avoid instanced more than one time, it needs to be
+				// checked again.
+				if (INSTANCE == null) {
+					INSTANCE = new LazySingleton();
+				}
+			}
+		}
+		return INSTANCE;
+	}
+}
+
+/**
+ * 
+ * @author YuCheng
+ *
+ */
+public class SingletonTest {
+	private final static Logger logger = LoggerFactory.getLogger(SingletonTest.class);
+
+	@Test
+	public void testSingleton() {
+		logger.debug("TEST Singleton");
+
+	}
+
+}