Unchecked conversion when popping stack Java

Question

I'm new to Java and have a question about a warning:

My general code:

private Stack<ArrayList> stackFrame = new Stack<ArrayList>();
private ArrayList<Object> curBlocKList = new ArrayList<Object>();
...
curBlockList = stackFrame.pop();

I'm getting:

Parser.java:78: warning: [unchecked] unchecked conversion
found   : java.util.ArrayList
required: java.util.ArrayList<java.lang.Object>
    curBlockList = stackFrame.pop();

I don't know how to syntactically make this work without a warning, as I'm working on a homework assignment and errors aren't allowed in compiling, and inserting

@SurpressWarning("unchecked")

is not allowed either.

What do I need to do to get rid of this warning?

Also, I want curBlocKList to hold a reference to the current top of the stack. Will this be accomplished by

curBlockList = stackFrame.pop();

or is there something else I need to do?

Answer 1

@SurpressWarning("unchecked") should be put before the method prototype to work.

But you should try to change

private Stack<ArrayList> stackFrame = new Stack<ArrayList>();

Into

private Stack<ArrayList<Object>> stackFrame = new Stack<ArrayList<Object>>();

Answer 2

You need to parameterize ArrayList within your parameterization of Stack. Also, I recommend using List instead of ArrayList; you should program to the interface, not the implementation.

private Stack<List<?>> stackFrame = new Stack<List<?>>();
private List<?> curBlockList = new ArrayList<Object>();