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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   * This code is free software; you can redistribute it and/or modify it
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   * published by the Free Software Foundation.  Oracle designates this
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   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
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   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
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  package java.util.function;
  
  import java.util.Objects;
  
  /**
   * Represents an operation on a single {@code double}-valued operand that produces
   * a {@code double}-valued result.  This is the primitive type specialization of
   * {@link UnaryOperator} for {@code double}.
   *
   * <p>This is a <a href="package-summary.html">functional interface</a>
   * whose functional method is {@link #applyAsDouble(double)}.
   *
   * @see UnaryOperator
   * @since 1.8
   */
  @FunctionalInterface
  public interface DoubleUnaryOperator {
  
      /**
       * Applies this operator to the given operand.
       *
       * @param operand the operand
       * @return the operator result
       */
      double applyAsDouble(double operand);
  
      /**
       * Returns a composed operator that first applies the {@code before}
       * operator to its input, and then applies this operator to the result.
       * If evaluation of either operator throws an exception, it is relayed to
       * the caller of the composed operator.
       *
       * @param before the operator to apply before this operator is applied
       * @return a composed operator that first applies the {@code before}
       * operator and then applies this operator
       * @throws NullPointerException if before is null
       *
       * @see #andThen(DoubleUnaryOperator)
       */
      default DoubleUnaryOperator compose(DoubleUnaryOperator before) {
          Objects.requireNonNull(before);
          return (double v) -> applyAsDouble(before.applyAsDouble(v));
      }
  
      /**
       * Returns a composed operator that first applies this operator to
       * its input, and then applies the {@code after} operator to the result.
       * If evaluation of either operator throws an exception, it is relayed to
       * the caller of the composed operator.
       *
       * @param after the operator to apply after this operator is applied
       * @return a composed operator that first applies this operator and then
       * applies the {@code after} operator
       * @throws NullPointerException if after is null
       *
       * @see #compose(DoubleUnaryOperator)
       */
      default DoubleUnaryOperator andThen(DoubleUnaryOperator after) {
          Objects.requireNonNull(after);
          return (double t) -> after.applyAsDouble(applyAsDouble(t));
      }
  
      /**
       * Returns a unary operator that always returns its input argument.
       *
       * @return a unary operator that always returns its input argument
       */
      static DoubleUnaryOperator identity() {
          return t -> t;
      }
  }
  