a Thunk Quiz

Thunk.java

abstract class Thunk<T> {
  private boolean evaluated;
  private T value;
  public T get() {
    if (!evaluated) {
      value = compute();
      evaluated = true;
    }
    return value;
  }
  abstract protected T compute();
}

Provide an alternate implementation of the following class (a Thunk - http://en.wikipedia.org/wiki/Thunk_%28functional_programming%29) that uses no conditional logic. For extra credit, make it thread-safe.
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