On a java TreeMap should i check size before clearing?

Question

I've assumed that i can just call clear instead of

if (tmap.size() > 0) {
    tmap.clear();
}

Or is one more efficient?

Answer 1

You will gain nothing because TreeMap.clear() is nothing in terms of overhead :

public void clear() {
    modCount++;
    size = 0;
    root = null;
}

So keep your code simple to read with just tmap.clear();

JDK collections classes are written to be optimized as much as possible.
So you generally don't need to worry about basic optimizations because these are bound to be done.
For example look at the HashMap.clear() logical, the clear() operation requires a little more overhead : clearing the table (buckets).
As a consequence, the size of the map is checked before performing that :

public void clear() {
    Node<K,V>[] tab;
    modCount++;
    if ((tab = table) != null && size > 0) {
        size = 0;
        for (int i = 0; i < tab.length; ++i)
            tab[i] = null;
    }
}