singleton-double-checked-locking

Author: ibrahimatay

README.md

@@ -12,7 +12,8 @@ Examples of design patterns in Java is presented in a way that is easy for human
 - Singleton
   - [Eager Instantiation](/singleton-eager-instantiation/src/main/java/com/ibrahimatay/Main.java)
   - [Lazy Instantiation](/singleton-lazy-instantiation/src/main/java/com/ibrahimatay/Main.java), 
-  - [Enum-based Singleton](/singleton-with-enum/src/main/java/com/ibrahimatay/Main.java)     
+  - [Enum-based Singleton](/singleton-with-enum/src/main/java/com/ibrahimatay/Main.java)  
+  - [Double Checked Locking](/singleton-double-checked-locking/src/main/java/com/ibrahimatay/Main.java)
 
 ## ***Structural***
 - [Adapter](/adapter/src/main/java/com/ibrahimatay/Main.java)

pom.xml

@@ -36,6 +36,7 @@
         <module>pipeline</module>
         <module>singleton-static-block</module>
         <module>singleton-thread-safe</module>
+        <module>singleton-double-checked-locking</module>
     </modules>
 
     <properties>

singleton-double-checked-locking/pom.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>com.ibrahimatay</groupId>
+        <artifactId>design-patterns</artifactId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>singleton-double-checked-locking</artifactId>
+
+    <properties>
+        <maven.compiler.source>23</maven.compiler.source>
+        <maven.compiler.target>23</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+</project>

singleton-double-checked-locking/src/main/java/com/ibrahimatay/Main.java

@@ -0,0 +1,46 @@
+package com.ibrahimatay;
+
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.List;
+import java.util.stream.IntStream;
+
+public class Main {
+    public static void main(String[] args) {
+        List<String> threads = List.of("Thread-1", "Thread-2", "Thread-3");
+
+        // Using Java Streams to run logging in parallel
+        threads.parallelStream().forEach(threadName -> {
+            Singleton logger = Singleton.getInstance();
+            IntStream.rangeClosed(1, 100).forEach(i -> {
+                logger.log(threadName + " - Log message " + i);
+                try {
+                    Thread.sleep(100); // Simulating delay
+                } catch (InterruptedException e) {
+                    e.printStackTrace();
+                }
+            });
+        });
+    }
+}
+
+class Singleton {
+    private static volatile Singleton instance;
+    private Singleton(){}
+
+    public static Singleton getInstance(){
+        if(instance==null){
+            synchronized (Singleton.class){
+                if (instance==null){
+                    instance = new Singleton();
+                }
+            }
+        }
+        return instance;
+    }
+
+    public void log(String message) {
+        String timeStamp = new SimpleDateFormat("HH:mm:ss.SSS").format(new Date());
+        System.out.println(timeStamp + " - " + message);
+    }
+}