import java.util.ArrayList;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.Lock;

public class KnivMonitor {
    
    private Lock laas = new ReentrantLock();
    private ArrayList<Kniv> knivHaug =  new ArrayList<Kniv>(); 

    public void settInn(Kniv kniv) {
        laas.lock();
        try {
            knivHaug.add(kniv);
        }
        finally {
            laas.unlock();
        }
    } 

    public Kniv[] taUtTo() {
        laas.lock();
        try {
            
            if (knivHaug.size() > 1) {
                Kniv[] kniver = new Kniv[2];
                kniver[0] = knivHaug.remove(0);
                kniver[1] = knivHaug.remove(0);
                return kniver;
            }
            else {
                return null;
            }
        }
        finally {
            laas.unlock();
        }
    }

    public int antall() {
        return knivHaug.size();
    }
}