Illustration of breaking Singleton pattern using Serialization & Deserialization

SingletonDeserializationExample.java

import java.io.*;

/**
 * Using Serialization & Deserialization, we can create new instance
 * thereby breaking SingletonPattern
 */
public class SingletonDeserializationExample implements Serializable {

    private static SingletonDeserializationExample single_instance = null;

    /**
     * Making the constructor as private
     */
    private SingletonDeserializationExample() {

    }

    /**
     * Static method to create instance of Singleton class
     * @return single object of 'SingletonDeserializationExample' class
     */
    public static SingletonDeserializationExample getInstance() {
        /**
         * Ensuring only one instance is created
         */
        if (single_instance == null)
            single_instance = new SingletonDeserializationExample();
        return single_instance;
    }

    public static void main(String[] args) throws IOException, ClassNotFoundException {

        /**
         * Serializing the object into byte stream and saving into a file
         */
        SingletonDeserializationExample objectOne = SingletonDeserializationExample.getInstance();
        ObjectOutput out = new ObjectOutputStream(new FileOutputStream("file.text"));
        out.writeObject(objectOne);
        out.close();

        /**
         * Deserializing the byte-stream from the file into a new object
         */
        ObjectInput in = new ObjectInputStream(new FileInputStream("file.text"));
        SingletonDeserializationExample objectTwo = (SingletonDeserializationExample) in.readObject();
        in.close();

        /**
         * Checking the hashCode for both the objects which would be different,
         * meaning the objects are different
         */
        System.out.println("Hashcode of Object 1 - " + objectOne.hashCode());
        System.out.println("Hashcode of Object 2 - " + objectTwo.hashCode());

    }

}