JAVA:通用函数X-> Y接口

here

public interface Function<T,R>

apply(Object)

T
R

Function interface

public interface Function<F, T> {
  /**
   * Applies the function to an object of type {@code F}, resulting in an object of     type {@code T}.
   * Note that types {@code F} and {@code T} may or may not be the same.
   *
   * @param from the source object
   * @return the resulting object
   */
  T apply(@Nullable F from);

  /**
   * Indicates whether some other object is equal to this {@code Function}. This     method can return
   * {@code true} <i>only</i> if the specified object is also a {@code Function} and, for every
   * input object {@code o}, it returns exactly the same value. Thus, {@code
   * function1.equals(function2)} implies that either {@code function1.apply(o)} and {@code
   * function2.apply(o)} are both null, or {@code function1.apply(o).equals(function2.apply(o))}.
   *
   * <p>Note that it is always safe <i>not</i> to override {@link Object#equals}.
   */
  boolean equals(@Nullable Object obj);
 }

Apache Commons Functor

T evaluate(A obj);

T evaluate(L left, R right);