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src/java.base/share/classes/java/util/function/Function.java

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   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.util.function;
  26 
  27 import java.util.Objects;
  28 
  29 /**
  30  * Represents a function that accepts one argument and produces a result.
  31  *
  32  * <p>This is a <a href="package-summary.html">functional interface</a>
  33  * whose functional method is {@link #apply(Object)}.
  34  *
  35  * @param <T> the type of the input to the function
  36  * @param <R> the type of the result of the function
  37  *
  38  * @since 1.8
  39  */
  40 @FunctionalInterface
  41 public interface Function<T, R> {
  42 
  43     /**
  44      * Applies this function to the given argument.
  45      *
  46      * @param t the function argument
  47      * @return the function result
  48      */
  49     R apply(T t);
  50 
  51     /**
  52      * Returns a composed function that first applies the {@code before}
  53      * function to its input, and then applies this function to the result.
  54      * If evaluation of either function throws an exception, it is relayed to
  55      * the caller of the composed function.
  56      *
  57      * @param <V> the type of input to the {@code before} function, and to the
  58      *           composed function
  59      * @param before the function to apply before this function is applied
  60      * @return a composed function that first applies the {@code before}
  61      * function and then applies this function
  62      * @throws NullPointerException if before is null
  63      *
  64      * @see #andThen(Function)
  65      */
  66     default <V> Function<V, R> compose(Function<? super V, ? extends T> before) {
  67         Objects.requireNonNull(before);
  68         return (V v) -> apply(before.apply(v));
  69     }
  70 
  71     /**
  72      * Returns a composed function that first applies this function to
  73      * its input, and then applies the {@code after} function to the result.
  74      * If evaluation of either function throws an exception, it is relayed to
  75      * the caller of the composed function.
  76      *
  77      * @param <V> the type of output of the {@code after} function, and of the
  78      *           composed function
  79      * @param after the function to apply after this function is applied
  80      * @return a composed function that first applies this function and then
  81      * applies the {@code after} function
  82      * @throws NullPointerException if after is null
  83      *
  84      * @see #compose(Function)
  85      */
  86     default <V> Function<T, V> andThen(Function<? super R, ? extends V> after) {
  87         Objects.requireNonNull(after);
  88         return (T t) -> after.apply(apply(t));
  89     }
  90 
  91     /**
  92      * Returns a function that always returns its input argument.
  93      *
  94      * @param <T> the type of the input and output objects to the function
  95      * @return a function that always returns its input argument
  96      */
  97     static <T> Function<T, T> identity() {
  98         return t -> t;
  99     }
 100 }


   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package javany.util.function;
  26 
  27 import java.util.Objects;
  28 
  29 /**
  30  * Represents a function that accepts one argument and produces a result.
  31  *
  32  * <p>This is a <a href="package-summary.html">functional interface</a>
  33  * whose functional method is {@link #apply(Object)}.
  34  *
  35  * @param <T> the type of the input to the function
  36  * @param <R> the type of the result of the function
  37  *
  38  * @since 1.8
  39  */
  40 @FunctionalInterface
  41 public interface Function<any T, any R> {
  42 
  43     /**
  44      * Applies this function to the given argument.
  45      *
  46      * @param t the function argument
  47      * @return the function result
  48      */
  49     R apply(T t);
  50 
  51     /**
  52      * Returns a composed function that first applies the {@code before}
  53      * function to its input, and then applies this function to the result.
  54      * If evaluation of either function throws an exception, it is relayed to
  55      * the caller of the composed function.
  56      *
  57      * @param <V> the type of input to the {@code before} function, and to the
  58      *           composed function
  59      * @param before the function to apply before this function is applied
  60      * @return a composed function that first applies the {@code before}
  61      * function and then applies this function
  62      * @throws NullPointerException if before is null
  63      *
  64      * @see #andThen(Function)
  65      */
  66     default <any V> Function<V, R> compose(Function<? super V, ? extends T> before) {
  67         Objects.requireNonNull(before);
  68         return (V v) -> apply(before.apply(v));
  69     }
  70 
  71     /**
  72      * Returns a composed function that first applies this function to
  73      * its input, and then applies the {@code after} function to the result.
  74      * If evaluation of either function throws an exception, it is relayed to
  75      * the caller of the composed function.
  76      *
  77      * @param <V> the type of output of the {@code after} function, and of the
  78      *           composed function
  79      * @param after the function to apply after this function is applied
  80      * @return a composed function that first applies this function and then
  81      * applies the {@code after} function
  82      * @throws NullPointerException if after is null
  83      *
  84      * @see #compose(Function)
  85      */
  86     default <any V> Function<T, V> andThen(Function<? super R, ? extends V> after) {
  87         Objects.requireNonNull(after);
  88         return (T t) -> after.apply(apply(t));
  89     }
  90 
  91     /**
  92      * Returns a function that always returns its input argument.
  93      *
  94      * @param <T> the type of the input and output objects to the function
  95      * @return a function that always returns its input argument
  96      */
  97     static <any T> Function<T, T> identity() {
  98         return t -> t;
  99     }
 100 }
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