ArrayList Thread Safe

ArrayListThreadSafe.java

import static java.util.concurrent.TimeUnit.MILLISECONDS;

import java.util.ArrayList;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public final class ArrayListThreadSafe {

	private final ArrayList<Object> array;
	private final AtomicInteger occupiedPositions;

	private final Lock readLock;
	private final Lock writeLock;

	public ArrayListThreadSafe() {
		array = new ArrayList<Object>();
		occupiedPositions = new AtomicInteger();

		ReentrantReadWriteLock rrwl = new ReentrantReadWriteLock();
		readLock = rrwl.readLock();
		writeLock = rrwl.writeLock();
	}

	public Object get(final int index, final long timeout, final TimeUnit timeUnit) {
		try {
			if (readLock.tryLock(timeout, timeUnit)) {
				return array.get(index);
			}
		} catch (InterruptedException e) {
			throw new IllegalStateException("unable to access the object", e);
		} finally {
			readLock.unlock();
		}
		throw new IllegalStateException("unable to access the object");
	}

	public void put(final int index, final Object element, final long timeout,
			final TimeUnit timeUnit) {
		try {
			if (writeLock.tryLock(timeout, timeUnit)) {
				occupiedPositions.incrementAndGet();
				array.add(index, element);
			}
		} catch (InterruptedException e) {
			throw new IllegalStateException("unable to access the object", e);
		} finally {
			writeLock.unlock();
		}
	}

	public int occupiedPositions() {
		return occupiedPositions.get();
	}

	public String toString() {
		return toString(100, MILLISECONDS);
	}

	public String toString(final long timeout, final TimeUnit timeUnit) {
		try {
			if (readLock.tryLock(timeout, timeUnit)) {
				return array.toString();
			}
		} catch (InterruptedException e) {
			throw new IllegalStateException("unable to access the object", e);
		} finally {
			readLock.unlock();
		}
		throw new IllegalStateException("unable to access the object");
	}
}