Using java.io.Serializable when implementing a tree?

Question

Hey everyone, I have ANOTHER serialization question, but this time it is in regards to Java's native serialization import when serializing to binary. I have to serialize a random tree that is generated in another java file. I know how serialization and deserialization works, but the example I followed when using binary serialization with java.io.Serializable did not work in the same fashion as when I did it with, say a simple object. Here is my code segment:

import java.io.*;
import java.io.FileInputStream;

public class BinaryS 
    {

    public static void main(String[] args) {
     Tree randomTree = RandomTreeBuilder.randomTree(10);

     FileOutputStream fOut=null;
     ObjectOutputStream oOut=null;

     try{
      fOut= new FileOutputStream("/Users/Pat/programs/binaryfile.txt");
      oOut = new ObjectOutputStream(fOut);
      oOut.writeObject(randomTree); //serializing randomTree
      System.out.println("An employee is serialized into /Users/Pat/binaryfile.txt");
     }catch(IOException e){
      e.printStackTrace();
     }finally{
      try {
       oOut.flush();
       oOut.close();
       fOut.close();
      } catch (IOException e1) {
       e1.printStackTrace();
      }
     }
    }
});

I believe the problem is when I use writeObject(randomTree). I get some terminal exceptions when this happens... they are below:

java.io.NotSerializableException: GeneralTree at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1081) at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:302) at BinaryS.main(BinaryS.java:24)

edit: I know it says GeneralTree, but at the start of the class it was in I put

print("public class RandomTreeBuilder implements java.io.Serializable");

then, GeneralTree is found below it

print(" protected static Tree tree;
protected static ArrayList names;
//e6.1

/**
 *Builds a random tree.  The build method does the work.
 */
//b6.2
public static Tree randomTree(int n) {
    // Create a random binary tree with n external nodes
    tree = new GeneralTree();
    names = NameGenerator.getNames();
    build(tree.getRoot(), n);  // auxiliary recursive method
    return tree;

");

Update: Hey guys, I figured out my own problem, turns out I am an idiot and didn't realize I had to download an additional .java file, an easy fix now! Thanks for your help!

Answer 1

At a guess, GeneralTree doesn't implement the Serializable marker interface, as documented here.

Actually, it could also be the objects you're storing in the tree aren't Serializable. A Collection is only serializable if all the elements in it are as well.

Answer 2

edit: I know it says GeneralTree, but at the start of the class it was in I put

print("public class RandomTreeBuilder implements java.io.Serializable");

This does you no good - you are not trying to write an object of type RandomTreeBuilder to the object stream; the type you are trying to write is GeneralTree and it is that class that must implement Serializable.

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FYI: in case you haven't come across it, this article covers many of the tricks and caveats of serialization: Discover the secrets of the Java Serialization API.