How to deserialize an object of ArrayList<String[]> in java

Question

I have serialized an ArrayList and stored it to a file with extension .ser . How can I deserialize the object and store it back into an ArrayList. I am getting an error Note: Hw5b.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details.

//Serializing Object
ArrayList<String[]> list = new ArrayList<String []>();
FileOutputStream fout =  new FileOutputStream("movie-matrix2.ser");
ObjectOutputStream oos = new ObjectOutputStream(fout);
oos.writeObject(list);

//Deserializing Object
FileInputStream streamIn = new FileInputStream("movie-matrix2.ser");
ObjectInputStream objectInputStream =  new  ObjectInputStream(streamIn);
list = (ArrayList<String[]>)objectInputStream.readObject();

JB Nizet · Accepted Answer · 2016-12-02 23:49:07Z

1

It's not an error. It's a warning.

For details, you could recompile with ecompile with -Xlint:unchecked, just as the message says.

But you can basically do nothing about that warning, except suppressing it: the compiler warns you that there is now way to ensure that the list you get is an ArrayList<String[]>. Only that it's an ArrayList.

answered Dec 2, 2016 at 23:49

JB Nizet

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2 Comments

VGR Over a year ago

There are workarounds: Cast to (ArrayList<?>) for example, then cast individual elements as needed. Or, avoid serializing a Collection at all, by instead writing list.toArray(new String[0][]).

JB Nizet Over a year ago

Yes, but that will make the code more complex, without brining any additional type safety.

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