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The AspectJ weaver applies aspects to Java classes. It can be used as a Java agent in order to apply load-time weaving (LTW) during class-loading and also contains the AspectJ runtime classes.
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// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
// 3. Neither the name of the copyright holders nor the names of its
//    contributors may be used to endorse or promote products derived from
//    this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
// THE POSSIBILITY OF SUCH DAMAGE.
package aj.org.objectweb.asm;

import java.util.Arrays;

/**
 * A constant whose value is computed at runtime, with a bootstrap method.
 *
 * @author Remi Forax
 */
public final class ConstantDynamic {

  /** The constant name (can be arbitrary). */
  private final String name;

  /** The constant type (must be a field descriptor). */
  private final String descriptor;

  /** The bootstrap method to use to compute the constant value at runtime. */
  private final Handle bootstrapMethod;

  /**
   * The arguments to pass to the bootstrap method, in order to compute the constant value at
   * runtime.
   */
  private final Object[] bootstrapMethodArguments;

  /**
   * Constructs a new {@link ConstantDynamic}.
   *
   * @param name the constant name (can be arbitrary).
   * @param descriptor the constant type (must be a field descriptor).
   * @param bootstrapMethod the bootstrap method to use to compute the constant value at runtime.
   * @param bootstrapMethodArguments the arguments to pass to the bootstrap method, in order to
   *     compute the constant value at runtime.
   */
  public ConstantDynamic(
      final String name,
      final String descriptor,
      final Handle bootstrapMethod,
      final Object... bootstrapMethodArguments) {
    this.name = name;
    this.descriptor = descriptor;
    this.bootstrapMethod = bootstrapMethod;
    this.bootstrapMethodArguments = bootstrapMethodArguments;
  }

  /**
   * Returns the name of this constant.
   *
   * @return the name of this constant.
   */
  public String getName() {
    return name;
  }

  /**
   * Returns the type of this constant.
   *
   * @return the type of this constant, as a field descriptor.
   */
  public String getDescriptor() {
    return descriptor;
  }

  /**
   * Returns the bootstrap method used to compute the value of this constant.
   *
   * @return the bootstrap method used to compute the value of this constant.
   */
  public Handle getBootstrapMethod() {
    return bootstrapMethod;
  }

  /**
   * Returns the number of arguments passed to the bootstrap method, in order to compute the value
   * of this constant.
   *
   * @return the number of arguments passed to the bootstrap method, in order to compute the value
   *     of this constant.
   */
  public int getBootstrapMethodArgumentCount() {
    return bootstrapMethodArguments.length;
  }

  /**
   * Returns an argument passed to the bootstrap method, in order to compute the value of this
   * constant.
   *
   * @param index an argument index, between 0 and {@link #getBootstrapMethodArgumentCount()}
   *     (exclusive).
   * @return the argument passed to the bootstrap method, with the given index.
   */
  public Object getBootstrapMethodArgument(final int index) {
    return bootstrapMethodArguments[index];
  }

  /**
   * Returns the arguments to pass to the bootstrap method, in order to compute the value of this
   * constant. WARNING: this array must not be modified, and must not be returned to the user.
   *
   * @return the arguments to pass to the bootstrap method, in order to compute the value of this
   *     constant.
   */
  Object[] getBootstrapMethodArgumentsUnsafe() {
    return bootstrapMethodArguments;
  }

  /**
   * Returns the size of this constant.
   *
   * @return the size of this constant, i.e., 2 for {@code long} and {@code double}, 1 otherwise.
   */
  public int getSize() {
    char firstCharOfDescriptor = descriptor.charAt(0);
    return (firstCharOfDescriptor == 'J' || firstCharOfDescriptor == 'D') ? 2 : 1;
  }

  @Override
  public boolean equals(final Object object) {
    if (object == this) {
      return true;
    }
    if (!(object instanceof ConstantDynamic)) {
      return false;
    }
    ConstantDynamic constantDynamic = (ConstantDynamic) object;
    return name.equals(constantDynamic.name)
        && descriptor.equals(constantDynamic.descriptor)
        && bootstrapMethod.equals(constantDynamic.bootstrapMethod)
        && Arrays.equals(bootstrapMethodArguments, constantDynamic.bootstrapMethodArguments);
  }

  @Override
  public int hashCode() {
    return name.hashCode()
        ^ Integer.rotateLeft(descriptor.hashCode(), 8)
        ^ Integer.rotateLeft(bootstrapMethod.hashCode(), 16)
        ^ Integer.rotateLeft(Arrays.hashCode(bootstrapMethodArguments), 24);
  }

  @Override
  public String toString() {
    return name
        + " : "
        + descriptor
        + ' '
        + bootstrapMethod
        + ' '
        + Arrays.toString(bootstrapMethodArguments);
  }
}