@Override
    public boolean isDone() {
        for (Future<Boolean> op : operands) {
            if (!op.isDone()) {
                return false;
            }
        }
        return true;
    }
<p>Adds a {@link CompletableFuture} to this conjunction. This can be called at any time, even after having called
{@link #get()} previously.</p>

@param operand The operand to add to this conjunction.
jdisc_core/src/main/java/com/yahoo/jdisc/handler/FutureConjunction.java