Is a deserialised object the same instance as the original

Question

When I instantiate an object from a class, an object is saved in the java heap. When I save the object by serializing it and I later deserialize the object, do I understand corr

Answer 1

No they will not be the same object in memory originalObj == deserilized will be false, however originalObj.equals(deserilized) should be true.

Objects B, C, D and E. All of them when instantiated, had Object A. Then, let's assume I serialize and deserialized all of them. When I change a field of Object A after deserialization, is there a way to reflect such change in the Object A(s) in BCDE?

If I understand you correctly the answer is no, the references will not be pointing to the same Object A

However if you so desire you can explicitly set all of the references of Object A in each object B, C, D and E to point to the same instance of Object A

Here is a demo to illustrate the points made.

import java.io.*;
import java.util.*;

public class Demo {  
  public static void main(String... aArguments) {  
    List quarks = Arrays.asList(
      new Quark("up"), new Quark("down")
    );

    serialize(quarks);
    List recoveredQuarks = deserialize();

    System.out.println(quarks == recoveredQuarks);               // false
    System.out.println(quarks.equals(recoveredQuarks));          // true

    System.out.println(quarks.get(0) == recoveredQuarks.get(0)); // false

    // but you can set it to the same instance
    recoveredQuarks.set(0, quarks.get(0));
    System.out.println(quarks.get(0) == recoveredQuarks.get(0)); // true

    quarks.get(0).name = "Charm";
    boolean b = quarks.get(0).name == recoveredQuarks.get(0).name;
    System.out.println(b);                                       // true
  }

  static void serialize(List quarks) {
    try {
      OutputStream file = new FileOutputStream("quarks.ser");
      OutputStream buffer = new BufferedOutputStream(file);
      ObjectOutput output = new ObjectOutputStream(buffer);
      output.writeObject(quarks);
      output.close();
    }
    catch(IOException ex) { ex.printStackTrace(); }
  }

  static List deserialize() {
    List recoveredQuarks = null;
    try {
      InputStream file = new FileInputStream("quarks.ser");
      InputStream buffer = new BufferedInputStream(file);
      ObjectInput input = new ObjectInputStream(buffer);
      recoveredQuarks = (List)input.readObject();
      input.close();
    } 
    catch(ClassNotFoundException ex){ }
    catch(IOException ex){ ex.printStackTrace(); }
    return recoveredQuarks;
  }
}

class Quark implements Serializable {
    String name;
    Quark(String name) {
      this.name = name;
    }

    @Override
    public boolean equals(Object o) {
      if (o != null && o instanceof Quark) {
        return this.name.equals(((Quark)o).name);
      }
      return false;
    }
}