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Google API Client Library for Java. Supports Java 5 (or higher) desktop (SE) and web (EE), Android, and Google App Engine.
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/*
 * Copyright (c) 2010 Google Inc.
 *
 * 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.api.client.util;

import com.google.common.base.Preconditions;

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.TreeSet;
import java.util.WeakHashMap;

/**
 * Parses class information to determine data key name/value pairs associated with the class.
 *
 * @since 1.0
 * @author Yaniv Inbar
 */
public final class ClassInfo {

  /** Class information cache. */
  private static final Map, ClassInfo> CACHE = new WeakHashMap, ClassInfo>();

  /**
   * Class.
   *
   * @deprecated (scheduled to be made private in 1.5) Use {@link #getUnderlyingClass()}
   */
  @Deprecated
  public final Class clazz;

  /** Map from {@link FieldInfo#getName()} to the field information. */
  private final IdentityHashMap nameToFieldInfoMap =
      new IdentityHashMap();

  /**
   * Unmodifiable sorted (with any possible {@code null} member first) list (without duplicates) of
   * {@link FieldInfo#getName()}.
   */
  final List names;

  /**
   * Returns the class information for the given underlying class.
   *
   * @param underlyingClass underlying class or {@code null} for {@code null} result
   * @return class information or {@code null} for {@code null} input
   */
  public static ClassInfo of(Class underlyingClass) {
    if (underlyingClass == null) {
      return null;
    }
    synchronized (CACHE) {
      ClassInfo classInfo = CACHE.get(underlyingClass);
      if (classInfo == null) {
        classInfo = new ClassInfo(underlyingClass);
        CACHE.put(underlyingClass, classInfo);
      }
      return classInfo;
    }
  }

  /**
   * Returns the underlying class.
   *
   * @since 1.4
   */
  public Class getUnderlyingClass() {
    return clazz;
  }

  /**
   * Returns the information for the given {@link FieldInfo#getName()}.
   *
   * @param name {@link FieldInfo#getName()} or {@code null}
   * @return field information or {@code null} for none
   */
  public FieldInfo getFieldInfo(String name) {
    return nameToFieldInfoMap.get(name == null ? null : name.intern());
  }

  /**
   * Returns the field for the given {@link FieldInfo#getName()}.
   *
   * @param name {@link FieldInfo#getName()} or {@code null}
   * @return field or {@code null} for none
   */
  public Field getField(String name) {
    FieldInfo fieldInfo = getFieldInfo(name);
    return fieldInfo == null ? null : fieldInfo.getField();
  }

  /**
   * Returns the underlying class is an enum.
   *
   * @since 1.4
   */
  public boolean isEnum() {
    return clazz.isEnum();
  }

  /**
   * Returns the number of fields associated with this data class.
   *
   * @deprecated (scheduled to be removed in 1.5) Use {@link #getNames()}{@code .size()}
   */
  @Deprecated
  public int getKeyCount() {
    return nameToFieldInfoMap.size();
  }

  /**
   * Returns the data key names associated with this data class.
   *
   * @deprecated (scheduled to be removed in 1.5) Use {@link #getNames()}
   */
  @Deprecated
  public Collection getKeyNames() {
    return names;
  }

  /**
   * Returns an unmodifiable sorted set (with any possible {@code null} member first) of
   * {@link FieldInfo#getName() names}.
   */
  public Collection getNames() {
    return names;
  }

  /**
   * Creates a new instance of the given class using reflection.
   *
   * @deprecated (scheduled to be removed in 1.5) use {@link Types#newInstance(Class)}
   */
  @Deprecated
  public static  T newInstance(Class clazz) {
    T newInstance;
    try {
      newInstance = clazz.newInstance();
    } catch (IllegalAccessException e) {
      throw handleExceptionForNewInstance(e, clazz);
    } catch (InstantiationException e) {
      throw handleExceptionForNewInstance(e, clazz);
    }
    return newInstance;
  }

  private static IllegalArgumentException handleExceptionForNewInstance(
      Exception e, Class clazz) {
    StringBuilder buf =
        new StringBuilder("unable to create new instance of class ").append(clazz.getName());
    if (Modifier.isAbstract(clazz.getModifiers())) {
      buf.append(" (and) because it is abstract");
    }
    if (clazz.getEnclosingClass() != null && !Modifier.isStatic(clazz.getModifiers())) {
      buf.append(" (and) because it is not static");
    }
    if (!Modifier.isPublic(clazz.getModifiers())) {
      buf.append(" (and) because it is not public");
    } else {
      try {
        clazz.getConstructor();
      } catch (NoSuchMethodException e1) {
        buf.append(" (and) because it has no public default constructor");
      }
    }
    throw new IllegalArgumentException(buf.toString(), e);
  }

  /**
   * Returns a new instance of the given collection class.
   * 
   * If a concrete collection class in the The class of the returned collection instance depends on
   * the input collection class as follows (first that matches):
   * 

   * {@code null} or {@link ArrayList} is an instance of the collection class: returns an
   * {@link ArrayList}
   * Concrete subclass of {@link Collection}: returns an instance of that collection class
   * {@link HashSet} is an instance of the collection class: returns a {@link HashSet}
   * {@link TreeSet} is an instance of the collection class: returns a {@link TreeSet}
   * 
   *
   * @param collectionClass collection class or {@code null} for {@link ArrayList}.
   * @return new collection instance
   * @deprecated (scheduled to be removed in 1.5) use {@link Data#newCollectionInstance(Type)}
   */
  @Deprecated
  public static Collection