What is the reverse of (ArrayList).toString for a Java ArrayList?

Question

I am using the toString method of ArrayList to store ArrayList data into a String. My question is, how do I go the other way? Is there an existing method that will parse the data in the String back into an ArrayList?

Answer 1

I would recommend using some standard format with a library for it instead.

JSON is probably the closest syntactically.

Alternatively some XML or serialization based solution could work too. It all depends on your needs of course.

Answer 2

Here's a similar question:

http://stackoverflow.com/questions/456367/reverse-parse-the-output-of-arrays-tostringint

It depends on what you're storing in the ArrayList, and whether or not those objects are easily reconstructed from their String representations.

Answer 3

The short answer is "No". There is no simple way to re-import an Object from a String, since certain type information is lost in the toString() serialization.

However, for specific formats, and specific (known) types, you should be able to write code to parse a String manually:

// Takes Strings like "[a, b, c]"
public List parse(String s) {
  List output = new ArrayList();
  String listString = s.substring(0, s.length - 1); // chop off brackets
  for (String token : new StringTokenizer(listString, ",")) {
    output.add(token.trim);
  }
  return output;
}

Reconstituting objects from their serialized form is generally called deserialization

Answer 4

What does the ArrayList consist of? As others said, it may be impossible in certain cases, but quite possible and guaranteed to work if:

• each string representation of element of the array can be identified unambiguously (as it can be for example if the ArrayList consists of Integers)

• there is a way to create an object of original type from its String representation. I find it most elegant to do this using a static method fromString

Of course, this mimics the whole (de)serialization framework.