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The core random number generators

There is a newer version: 0.7

package prng.seeds;

import java.util.concurrent.Callable;

/**
 * A seed whose data is only derived when it is actually needed.
 *
 * @author Simon Greatrix
 */
public class DeferredSeed extends Seed {

  /** Source of the seed for when it is needed */
  private final Callable source;


  /**
   * Create a deferred seed
   *
   * @param name the name of the seed
   * @param source the source of the seed data
   */
  public DeferredSeed(String name, Callable source) {
    super(name, null);
    this.source = source;
  }


  /**
   * Derive the seed and return a copy of it
   */
  @Override
  public byte[] getSeed() {
    init();
    return super.getSeed();
  }


  /**
   * Initialise this seed with actual data
   */
  private void init() {
    if (data != null) {
      return;
    }
    try {
      data = source.call();
    } catch (Exception e) {
      SeedStorage.LOG.error("Failed to create seed \"{}\" from {}", name,
          source.getClass().getName(), e);
      data = new byte[0];
    }
  }


  /**
   * This should never be saved, so it cannot be initialized from input. This method throws an UnsupportedOperationException.
   *
   * @param input ignored
   */
  @Override
  public void initialize(SeedInput input) {
    throw new UnsupportedOperationException();
  }


  /**
   * {@inheritDoc}
   */
  @Override
  public void save(SeedOutput output) {
    init();
    super.save(output);
  }

}