Thread: Java Serialization / Deserialization Duplicate Object Problem

I'm writing a large scale program in java where I keep track of the Nodes with different data structures.

Specifically, one of my Node type have 2 left & right pointers for 2 different Binary Search Trees and I also keep track of that Node in a priority queue.

I have to serialize and deserialize my program to be able to use it for multiple times despite shutdown.

The problem is, when I insert a Node in my program and check the same node in the 3 different structures (2 BSTs and 1 Heap) it's the same exact Node as it should be (I'm using the pointers in the Node to construct BST and it's a part of the heap array).

But whenever I restart my program (serialize / deserilaize) and check the "supposed to be same" Node in the structures, I see 3 duplicates rather than 1 node with the same memory location. My code is definitely creating duplicates while the save/load process.

Here's an outline of my loading (deserilaize) function:

public BSTStructure load() {
        BSTStructure bstStructure = null;
        try {
            File file = new File("filepath");
            boolean fileCreated = file.createNewFile();
            FileInputStream fileInput = new FileInputStream(file);
            ObjectInputStream in = new ObjectInputStream(fileInput);
            bstStructure = (BSTStructure) in.readObject();
            fileInput.close();
            in.close();
            return bstStructure;
        } catch (FileNotFoundException e) {
            System.out.println("filepath file is not found");
        } catch (ClassNotFoundException e) {
            System.out.println("Class not found");
        } catch (EOFException e) {
            System.out.println("file is Empty");
            bstStructure = new BSTSTructre();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return moviesByID;
    }
 
public void save(BSTStructre bstStructure) {
        try {
            FileOutputStream file = new FileOutputStream("filepath");
            ObjectOutputStream out = new ObjectOutputStream(file);
            out.writeObject(bstStructure);
            out.close();
            file.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

My save/load functions for the other data structures are similar.

I hope that you can help me with this.

I narrowed down my problem from a +2000 lines of code to this specific issue.

I can't reproduce the issue unless I restart (save / load) the program.

It seems like you're encountering a problem with object duplication during the serialization and deserialization process in your Java program. When you serialize an object and then deserialize it back, you expect to get the same object instance, but instead, you're getting duplicate instances.

This issue likely arises because Java's serialization mechanism does not preserve object identity by default. Each time you deserialize an object, a new instance is created, even if the object was the same one that was serialized. Therefore, you're seeing duplicates of the same node in your data structures after deserialization.

To address this problem, you can implement custom serialization logic in your Node class to ensure that object identity is preserved during the serialization and deserialization process. One way to achieve this is by using the `writeObject()` and `readObject()` methods in your Node class to control how the object is serialized and deserialized.

Here's an outline of how you can modify your Node class to preserve object identity:

```java
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

public class Node implements Serializable {
private static final long serialVersionUID = 1L;

// Your Node implementation

private void writeObject(ObjectOutputStream out) throws IOException {
// Serialize the node's data and any other necessary fields
out.defaultWriteObject();
}

private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
// Deserialize the node's data and any other necessary fields
in.defaultReadObject();
}
}
```

By implementing custom serialization logic in this way, you can ensure that when you deserialize a Node object, you get the same instance as the one that was serialized, thus preventing duplicates in your data structures.

After making these changes, you should see consistent behavior across multiple program executions, even after serialization and deserialization. If you need help with Java assignment work, don't hesitate to seek help from online resources or communities specializing in programming education and support. There are various platforms out there where you can find expert assistance tailored to your specific needs, ensuring smooth progress with your programming tasks like ProgrammingHomeworkHelp.com.