How to make object array of varying length?

Question

I am making an ArrayList of objects that will be displayed in a ListView. When I use Object[] ObjectList = new Object[length] it expects an exact length for the entire array upon creation. I have tried making the value of the length an int variable but it appears it doesn't update the length when the variable is changed. How can I accomplish this? I am kinda new to Java, so thanks to anyone who helps out!

Answer 1

Use List interface of Collections framework. E.g. List<String> data = new ArrayList<>(). You can conver it to array if you need with data.toArray() method

Answer 2

Arrays have a fixed size. Once an array is created, the size can't be changed any more. You can only create a new array and change the reference your variable is holding!

In other words - assume you start with:

Object[] items = new Object[5];

Later you figure: I need more space:

Object[] moreItems = new Object[15];

And then you can use System.arraycopy() to copy the content of the first array into the second.

For the record:

• List/ArrayList are not Arrays.
• ArrayList uses the approch described above under the covers to implement that "dynamically" growing array experience for you

Answer 3

I will not repeat what others have very well said.

About your actual problem, android.widget.ListView is designed to be populated with array type.
Now if data used to populate the ListView have a size variable and may often changed, you have an alternative : using an ArrayList wrapped in an ArrayAdapter.

During the onCreate() method you could create the adapter and set it to the ListView :

List<String> list = new ArrayList<>();
...
ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(
                 this, 
                 android.R.layout.listview,
                 arrayList);
listView.setAdapter(arrayAdapter); 

Now, you don't have any longer the problem of the fixed size array as you use an ArrayList that doesn't have this limitation.