Question

Why this piece of code does not work? How to set the length of Object[].

Object[] entry = new Object[]{};
entry[0] = 1;
entry[1] = "1";

Answer 1

If you are Initializing a new array then you either have to specify its size explicitly using the syntax mentioned in the answer above:

Object[] entry = new Object[2];

or use the array initializer block what you presented in your question like this:

Object[] entry = new Object[] {"a", "b"};

What you did here was initializing an array to be empty thus setting its size to 0. If you print out the length of that array it will be 0.

If you want an array whose size can be modified you are advised to use the List interface (an ArrayList for example).

List<Object> myList = new ArrayList<Object>();

You can set the initial capacity of an ArrayList using its constructor:

List<Object> myList = new ArrayList<Object>(2);

List is generic so you should use the type parameter otherwise you will get some warnings.

If you don’t know what objects will you store in your List you may do something like this:

List<?> myList = new ArrayList(2);

but you will get warnings that way.

More info about arrays: Arrays

And about Lists: List interface

If you are interested in java Generics: Generics