Question

i search a way to copy x element from a map to another.
i tried this code

private void newMapElement( Map<?, ?> userMap, Map<?, ?> newUserMap, int maxSize)
{
    int i = 0;
    for ( Map.Entry<?, ?> entry : userMap.entrySet() )
    {
        newUserMap.put( entry.getKey(), entry.getValue() );
            i++;
            if ( i == maxSize)
            {
                break;
            }
    }
}

but java don’t seem to like the put.

Any idea?

Answer 1

you have to use ? super T for newUserMap as wildcards with super(wildcards with upperbounds) would allow you to add elements into your map,your code should be something like below:

private <T> void newMapElement( Map<? extends T, ? extends T> userMap, Map<? super T, ? super T> newUserMap, int maxSize)
{
    int i = 0;
    for ( Map.Entry<? extends T, ? extends T> entry : userMap.entrySet() )
    {
        newUserMap.put( entry.getKey(), entry.getValue() );
            i++;
            if ( i == maxSize)
            {
                break;
            }
    }
}