CODEWITHSUNDEEP
javaoopdesign-patterns
codegeek
codegeek

Reputation: 49

Same instance sharing with multiple requests in Java (OOP)

I have one class whose single instance needs to be used by multiple classes in Java. I found two solutions for the same: 1. Pass the instance as method parameters 2. Use Static factory

My question is if I used static factory, how can I differentiate the incoming requests when I am using the static method. I want to avoid the 1st solution as there are many classes that are going to use this instance. Also, recommend the best design if other than mentioned above.

Code Example:

 class MyClass{


        Map<String, List<String>> myMap=new ConcurrentHashMap();

           public static void addToMap(String key, String value){
              if(myMap.containsKey(key)){
                  List<String> stringList=myMap.get(key);
                 stringList.add(value);
               }
               else{
                 myMap.put(key,value);
               }
           }
    }

I want to perform this add method at many places while program execution for eg:

Method addEmployee():

if(employeeName==null){
   MyClass.addToMap("ER101", "Name Error");
}
Method insertInDB():
catch(SQLException e){
   MyClass.addToMap("SQL", "Error Occurred in DB Operation");
}

Thanks

Upvotes: 0

Views: 1094

Answers (3)

JVN
JVN

Reputation: 239

The best design would be to make your class as Singleton class. For your usage i think you can follow the below steps,

  • make your constructor as private.

  • then, have a static function inside that class to return the instantiated object of your class.

  • you can have your own if(classobj==nul) check to verify if its already instantiated or not(only on first call it will be null , further calls it wont be null) and return the object.

Cheers :)

Upvotes: 0

Fiid
Fiid

Reputation: 1840

There are a number of ways to make the same instance of a class available to different callers such as threads or requests.

One of the easiest things you can do is create a singleton as shown above. The problem with singletons is that there can only ever be one of them, as they are generally set up to enforce that there is a single instance of them.

Better is to create your instance, and pass it to the things that need it. If you're creating a web application or similar, you can use a Dependency Injection framework such as SpringFramework to achieve this.

Injecting your instance where it is needed will mean it will be easier to replace this instance with a dummy instance for testing, and during testing you'll be able to create many instances of this class configured in different ways to test.

Upvotes: 2

melli-182
melli-182

Reputation: 1234

As 12dollar says: Use the Singleton Design Pattern, and ask for that instance to the Singleton Class:

public class ClassicSingleton {
   private static ClassicSingleton instance = null;
   protected ClassicSingleton() {
      // Exists only to defeat instantiation.
   }
   public static ClassicSingleton getInstance() {
      if(instance == null) {
         instance = new ClassicSingleton();
      }
      return instance;
   }
}

Then you could call getInstance().

Upvotes: 0

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