Counter.java

/**
 * A Counter can issue sequential ids, and return the largest id issued so far.
 */
public class Counter {
    private long nextValue = 0;

    /**
     * @return the next value from this counter.
     */
    public long nextValue() {
        final long thisValue = nextValue;
        nextValue++;
        return thisValue;
    }

    /**
     * @return the highest value returned so far by this counter.
     */
    public long maxValueAssigned() {
        return nextValue - 1;
    }
}