Yes, but only if all threads access the same file, and you are using a custom implementation (not java.io.File, perhaps a wrapper)

the singleton pattern is a design pattern that is used to restrict instantiation of a class to one object

Singletons (being often a bad choice) are classes that can have only one instance throughout the whole program.

For example a SingletonConfigFile might look like this. Have in mind that:

• it is for reading one file only. It would make sense for this to be a config file.
• if your class can be instantiated more than once, for different files, it is not singleton.
• don't use this code - it doesn't take into account concurrency problems which are a whole different area of discussion.

.

public SingletonConfigFile {
   private static String filename = "config.xml";
   private File file;
   private static SingletonConfigFile instance;

   private SingletonConfigFile() {
       if (instance != null) {
           throw new Error();
       }
       file = new File(filename);
   }

   public synchronized SingletonConfigFile getInstance() {
      if (instance == null) {
          instance = new SignletonConfigFile();
      }
      return instance
   }

   public String read() {
       // delegate to the underlying java.io.File
   }
}

But this example is on the edge of sense. Singletons are used in cases when there is only one object (as I stated above). For example it would make sense to have:

• RingOfPower.getInstance() - there is only one ring of power (Sauron's), and there can't exist more.
• Sun.getInstance() - only one star called "sun".
• all objects in the withing of your application that logically should exist only once - a registry, an application context, etc.

In some cases, we need to expose a shared resource throughout the application e.g. DB connection but we don't want to

1. create shared object up-front (before creation of client objects).
2. explicitly pass shared object to each client object.

then we can use Singleton design pattern.

Typical Singleton class looks like

public class MySingleton {
      private MySingleton INSTANCE
      private MySingleton() {
      }

      public static MySingleton getInstance() {
       if (INSTANCE == null) {
         syncronized (MySingleton.class) {
           if (INSTANCE == null) {
             INSTANCE = new MySingleton();
           }
         }
       }
       return INSTANCE;
      }
     // instance methods exposing business operation
    }

But we can achieve the similar behaviour by making each and every instance methods which are exposing business operation as static. In this approach we don't even need to create single object.
Then why do we need Singleton?
Well, the answer is simple. To isolate actual implementation from the client. Basically we are applying abstraction OOP principle here.
This is helpful If the singleton class is part of library which is used by various clients and library wants to vary the implementation as per the client.

Sample for such singleton can be

public class MySingleton {
      private MySingleton INSTANCE
      private MySingleton() {
      }

      public static MySingleton getInstance() {
       if (INSTANCE == null) {
         syncronized (MySingleton.class) {
           if (INSTANCE == null) {
             INSTANCE = new MySingletonChild(); // here we are creating an object of subclass of MySingleton.
           }
         }
       }
       return INSTANCE;
      }
     // instance methods exposing business operation
    }

Hope this help in understanding Singleton design pattern.