Class Converter

output/java_guava/1.4.17/Converter.java:110–546

A function from A to B with an associated reverse function from B to A; used for converting back and forth between different representations of the same information . Invertibility The reverse operation may be a strict inverse

@Beta
@GwtCompatible
public abstract class Converter<A, B> implements Function<A, B> {
  private final boolean handleNullAutomatically;

  // We lazily cache the reverse view to avoid allocating on every call to reverse().

  private transient Converter<B, A> reverse;

  /** Constructor for use by subclasses. */


  protected Converter() {
    this(true);
  }

  /**
   * Constructor used only by {@code LegacyConverter} to suspend automatic null-handling.
   */

  Converter(boolean handleNullAutomatically) {
    this.handleNullAutomatically = handleNullAutomatically;
  }

  // SPI methods (what subclasses must implement)

  /**
   * Returns a representation of {@code a} as an instance of type {@code B}. If {@code a} cannot be
   * converted, an unchecked exception (such as {@link IllegalArgumentException}) should be thrown.
   *
   * @param a the instance to convert; will never be null
   * @return the converted instance; <b>must not</b> be null
   */


  protected abstract B doForward(A a);

  /**
   * Returns a representation of {@code b} as an instance of type {@code A}. If {@code b} cannot be
   * converted, an unchecked exception (such as {@link IllegalArgumentException}) should be thrown.
   *
   * @param b the instance to convert; will never be null
   * @return the converted instance; <b>must not</b> be null
   * @throws UnsupportedOperationException if backward conversion is not implemented; this should be
   *     very rare. Note that if backward conversion is not only unimplemented but
   *     unimplement<i>able</i> (for example, consider a {@code Converter<Chicken, ChickenNugget>}),
   *     then this is not logically a {@code Converter} at all, and should just implement {@link
   *     Function}.
   */


  protected abstract A doBackward(B b);

  // API (consumer-side) methods

  /**
   * Returns a representation of {@code a} as an instance of type {@code B}.
   *