Re: Generic generics help
wizard of oz wrote:
public class SparseMatrix<R, C, E> {
private TreeSet<R> rowHeaders = new TreeSet<R> ();
private TreeSet<C> colHeaders = new TreeSet<C> ();
public void add (R rowKey, C colKey, E element) {
ensureExists (rowHeaders, rowKey);
ensureExists (colHeaders, colKey);
}
private void ensureExists (TreeSet<? extends Object> treeSet, Object
The problem is that the compiler is complaining about the treeSet.add
Well, the problem is that "rowHeaders" and "colHeaders" contain types of
R and C respectively, and you're trying to add a type of Object.
If you want to ensure that some type R "rowKey" exists in rowHeaders, then
boolean exists = rowHeaders.contains( rowKey );
will do the whole thing for you. I think however you are confused as to
what a Set like TreeSet will actually do for you. You seem to be trying
to ensure that the /pair/ R, E exists, in which case you need a Map, not
a Set.
E tempElement;
if( (tempElement = rowMap.get( rowKey )) != null ) {
// the pair (rowKey, element) exist
}
You might even put rowKey and colKey together in one single object
though and just do look-ups on that. Faster and easier.
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