Thread Safe map wrapper scratch

ThreadSafeMap.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.stream.IntStream;

class Scratch {

  static class ThreadSafeMap<K, V> {
    private final Map<K, V> map = new HashMap<>();
    private final ReadWriteLock lock = new ReentrantReadWriteLock();
    private final Lock readLock = lock.readLock();
    private final Lock writeLock = lock.writeLock();

    public void put(final K key, final V value) {
      writeLock.lock();
      try {
        System.out.println("writing " + key + " with " + value);
        map.put(key, value);
      } finally {
        writeLock.unlock();
      }
    }

    public V[] valuesArray(V[] array) {
      readLock.lock();
      try {
        return map.values().toArray(array);
      } finally {
        readLock.unlock();
      }
    }

    public Collection<V> values() {
      readLock.lock();
      try {
        return new ArrayList<>(map.values());
      } finally {
        readLock.unlock();
      }
    }
  }

  public static void main(String[] args) {
    var map = new ThreadSafeMap<Integer, Integer>();

    var writeThread = new Thread(() -> {
      int counter = 0;
      while (true) {
        try {
          Thread.sleep(10);
          counter++;
          map.put(counter, counter);
        } catch (Exception e) {
          System.err.println("Something went wrong in WRITE thread: " + e.getMessage());
          e.printStackTrace();
        }
      }
    });

    var readThread = new Thread(() -> {
      while (true) {
        try {
//        var sum = Arrays.stream(map.valuesArray(new Integer[]{})).reduce(Integer::sum);
          var sum = map.values().stream().reduce(Integer::sum);
          System.out.println("Summing values result: " + sum);
          Thread.sleep(10);
        } catch (Exception e) {
          System.err.println("Something went wrong in READ thread: " + e.getMessage());
          e.printStackTrace();
        }
      }
    });

    readThread.start();
    writeThread.start();

    System.out.println("Threads started!");
  }
}