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Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. Guava has only one code dependency - javax.annotation, per the JSR-305 spec.

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/*
 * Copyright (C) 2005 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.reflect;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;

/**
 * Static utilities relating to Java reflection.
 *
 * @since 12.0
 */
@Beta
public final class Reflection {

  /**
   * Returns the package name of {@code clazz} according to the Java Language Specification (section
   * 6.7). Unlike {@link Class#getPackage}, this method only parses the class name, without
   * attempting to define the {@link Package} and hence load files.
   */
  public static String getPackageName(Class clazz) {
    return getPackageName(clazz.getName());
  }

  /**
   * Returns the package name of {@code classFullName} according to the Java Language Specification
   * (section 6.7). Unlike {@link Class#getPackage}, this method only parses the class name, without
   * attempting to define the {@link Package} and hence load files.
   */
  public static String getPackageName(String classFullName) {
    int lastDot = classFullName.lastIndexOf('.');
    return (lastDot < 0) ? "" : classFullName.substring(0, lastDot);
  }

  /**
   * Ensures that the given classes are initialized, as described in
   * 
   * JLS Section 12.4.2.
   *
   * WARNING: Normally it's a smell if a class needs to be explicitly initialized, because static
   * state hurts system maintainability and testability. In cases when you have no choice while
   * inter-operating with a legacy framework, this method helps to keep the code less ugly.
   *
   * @throws ExceptionInInitializerError if an exception is thrown during
   *   initialization of a class
   */
  public static void initialize(Class... classes) {
    for (Class clazz : classes) {
      try {
        Class.forName(clazz.getName(), true, clazz.getClassLoader());
      } catch (ClassNotFoundException e) {
        throw new AssertionError(e);
      }
    }
  }

  /**
   * Returns a proxy instance that implements {@code interfaceType} by
   * dispatching method invocations to {@code handler}. The class loader of
   * {@code interfaceType} will be used to define the proxy class. To implement
   * multiple interfaces or specify a class loader, use
   * {@link Proxy#newProxyInstance}.
   *
   * @throws IllegalArgumentException if {@code interfaceType} does not specify
   *     the type of a Java interface
   */
  public static  T newProxy(
      Class interfaceType, InvocationHandler handler) {
    checkNotNull(handler);
    checkArgument(interfaceType.isInterface(), "%s is not an interface", interfaceType);
    Object object = Proxy.newProxyInstance(
        interfaceType.getClassLoader(),
        new Class[] { interfaceType },
        handler);
    return interfaceType.cast(object);
  }

  private Reflection() {}
}