Java Serialization Comparator

Question

Hello,

Is it possible to serialize a TreeMap with a comparator??

I've tested and it serializes well a treemap without comparator, when you add the comparator, it throws an exception.

If I declare comparator as transient, it still doesn't work. It only works if I make every tree map transient but it doesnt serialize the trees in that case.

Answer 1

All the classes which you attempt to serialize must implement the java.io.Serializable interface. Also, each member variable in your class should be Serializable. In fact, your whole hierarchy should be.

Answer 2

They all do, it gives error in this classe.

Answer 3

For more help, look at this. Other things to consider (as mentioned in this document and elsewhere):

• versioning
• custom serial forms for objects
• what fields of your object should be serialized and which ones are transient

Answer 4

You might find that it is as simple as changing the Comparator field to a static rather than an instance member:

public final static Comparator<String> ID_IGN_CASE_COMP

You will need to make sure that all the other fields are Serializable but this should be a start.

Answer 5

Going from your comment on some other answers:

How can you declare the comparator transient? You can't modify the field in the TreeMap that saves it. What happens if you make the Comparator implement Serializable?

Answer 6

TreeMap isn't doing anything special, here. If the only difference between a TreeMap that serializes and one that doesn't is your comparator... then your comparator is not serializable.

How are you implementing the comparator? Your transient declaration is meaningless to the TreeMap class which does not have a transient reference.

What does the exception say?