How to read and write a HashMap to a file?

Question

I have the following HashMap:

HashMap fileObj = new HashMap();

ArrayList cols         


        

Answer 1

You appear to be confusing the internal resprentation of a HashMap with how the HashMap behaves. The collections are the same. Here is a simple test to prove it to you.

public static void main(String... args)
                            throws IOException, ClassNotFoundException {
    HashMap fileObj = new HashMap();

    ArrayList cols = new ArrayList();
    cols.add("a");
    cols.add("b");
    cols.add("c");
    fileObj.put("mylist", cols);
    {
        File file = new File("temp");
        FileOutputStream f = new FileOutputStream(file);
        ObjectOutputStream s = new ObjectOutputStream(f);
        s.writeObject(fileObj);
        s.close();
    }
    File file = new File("temp");
    FileInputStream f = new FileInputStream(file);
    ObjectInputStream s = new ObjectInputStream(f);
    HashMap fileObj2 = (HashMap) s.readObject();
    s.close();

    Assert.assertEquals(fileObj.hashCode(), fileObj2.hashCode());
    Assert.assertEquals(fileObj.toString(), fileObj2.toString());
    Assert.assertTrue(fileObj.equals(fileObj2));
}