Thread security Singleton agency a Singleton course of teaching which returns just same instance fifty-fifty if exposed to multiple threads. Singleton inwards Java has been a classical pattern pattern similar Factory method pattern or Decorator pattern pattern too has been used a lot fifty-fifty within JDK similar java.lang.Runtime is an instance of Singleton class. Singleton pattern ensures that just 1 instance of course of teaching volition rest inwards Java plan at whatsoever time. In our lastly postal service 10 Interview questions on Singleton inwards Java nosotros convey discussed many unlike questions asked on Singleton pattern, One of them was writing Thread security singleton inwards Java. Prior to Java v double checked locking machinery is used to create thread-safe singleton inwards Java which breaks if 1 Thread doesn't run across instance created past times other thread at same fourth dimension too eventually you lot volition halt upwardly amongst to a greater extent than than 1 instance of Singleton class. From Java v onwards volatile variable guarantee tin live used to write thread security singleton past times using double checked locking pattern. I personally don't prefer that way every bit in that place are many other simpler alternatives to write thread-safe singleton is available available similar using static field to initialize Singleton instance or using Enum every bit Singleton inwards Java. Let’s run across instance of both ways to create thread-safe Singleton inwards Java.
Java Singleton Example – Thread security Singleton inwards Java using Enum
10 Examples of Enum inwards Java. Using Enum to create Singleton is past times far most uncomplicated too effective way to create thread-safe Singleton inwards Java, every bit thread-safety guarantee is provided past times Java programming linguistic communication itself. You don't demand to bother virtually thread-safety issue. Since Enum instances are past times default final inwards Java, it every bit good provides security against multiple instance due to serialization.
One indicate which is worth remembering is that, when nosotros beak virtually thread-safe Singleton, nosotros are talking virtually thread-safety during instance creation of Singleton course of teaching too non when nosotros telephone telephone whatsoever method of Singleton class. If your Singleton course of teaching keep whatsoever country too contains method to modify that state, you lot demand to write code to avoid too thread-safety too synchronization issues. Any way hither is code example of creating thread security Singleton inwards Java using Enum.
One indicate which is worth remembering is that, when nosotros beak virtually thread-safe Singleton, nosotros are talking virtually thread-safety during instance creation of Singleton course of teaching too non when nosotros telephone telephone whatsoever method of Singleton class. If your Singleton course of teaching keep whatsoever country too contains method to modify that state, you lot demand to write code to avoid too thread-safety too synchronization issues. Any way hither is code example of creating thread security Singleton inwards Java using Enum.
public enum Singleton{
INSTANCE;
public void show(){
System.out.println("Singleton using Enum inwards Java");
}
}
INSTANCE;
public void show(){
System.out.println("Singleton using Enum inwards Java");
}
}
//You tin access this Singleton every bit Singleton.INSTANCE too telephone telephone whatsoever method similar below
Singleton.INSTANCE.show();
If this suits your demand than this is the most slow way of writing thread-safe Singleton inwards Java. Using Enum every bit Singleton every bit good furnish yoke of to a greater extent than benefits which you lot tin uncovering out on Why Enum Singleton are ameliorate inwards Java.
Java Singleton Example - Thread Safe Singleton using Static plain Initialization
You tin every bit good create thread security Singleton inwards Java past times creating Singleton instance during class loading. static fields are initialized during course of teaching loading too Classloader volition guarantee that instance volition non live visible until its fully created. Here is instance of creating thread security singleton inwards Java using static mill method. Only disadvantage of this implementing Singleton patter using static plain is that this is not a lazy initialization too Singleton is initialized fifty-fifty earlier whatsoever clients telephone telephone in that place getInstance() method.
public class Singleton{
private static final Singleton INSTANCE = new Singleton();
private Singleton(){ }
public static Singleton getInstance(){
return INSTANCE;
}
public void show(){
System.out.println("Singleon using static initialization inwards Java");
}
}
private static final Singleton INSTANCE = new Singleton();
private Singleton(){ }
public static Singleton getInstance(){
return INSTANCE;
}
public void show(){
System.out.println("Singleon using static initialization inwards Java");
}
}
//Here is how to access this Singleton class
Singleton.getInstance().show();
here nosotros are non creating Singleton instance within getInstance() method instead it volition live created past times ClassLoader. Also private constructor makes impossible to create around other instance , except 1 case. You tin nevertheless access individual constructor past times reflection too calling setAccessible(true). By the way You tin nevertheless foreclose creating around other instance of Singleton past times this way past times throwing Exception from constructor.
Further Learning
Multithreading too Parallel Computing inwards Java
Java Concurrency inwards Practice - The Book
What is Observer pattern inwards Java amongst existent footing Example