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Java example source code file (AssistedConstructor.java)

This example Java source code file (AssistedConstructor.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

annotation, arraylist, assistedconstructor, constructor, invocationtargetexception, list, override, parameterlistkey, reflection, set, string, throwable, util

The AssistedConstructor.java Java example source code

 * Copyright (C) 2007 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,
 * See the License for the specific language governing permissions and
 * limitations under the License.

package com.google.inject.assistedinject;

import com.google.common.collect.Lists;
import com.google.inject.Inject;
import com.google.inject.TypeLiteral;

import java.lang.annotation.Annotation;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

 * Internal respresentation of a constructor annotated with
 * {@link AssistedInject}
 * @author jmourits@google.com (Jerome Mourits)
 * @author jessewilson@google.com (Jesse Wilson)
class AssistedConstructor<T> {

  private final Constructor<T> constructor;
  private final ParameterListKey assistedParameters;
  private final List<Parameter> allParameters;
  public static <T> AssistedConstructor create(
      Constructor<T> constructor, List> parameterTypes) {
    return new AssistedConstructor<T>(constructor, parameterTypes);

  private AssistedConstructor(Constructor<T> constructor, List> parameterTypes) {
    this.constructor = constructor;

    Annotation[][] annotations = constructor.getParameterAnnotations();

    List<Type> typeList = Lists.newArrayList();
    allParameters = new ArrayList<Parameter>();

    // categorize params as @Assisted or @Injected
    for (int i = 0; i < parameterTypes.size(); i++) {
      Parameter parameter = new Parameter(parameterTypes.get(i).getType(), annotations[i]);
      if (parameter.isProvidedByFactory()) {
    this.assistedParameters = new ParameterListKey(typeList);
   * Returns the {@link ParameterListKey} for this constructor.  The
   * {@link ParameterListKey} is created from the ordered list of {@link Assisted}
   * constructor parameters.
  public ParameterListKey getAssistedParameters() {
    return assistedParameters;
   * Returns an ordered list of all constructor parameters (both
   * {@link Assisted} and {@link Inject}ed).
  public List<Parameter> getAllParameters() {
    return allParameters;

  public Set<Class getDeclaredExceptions() {
    return new HashSet<Class(Arrays.asList(constructor.getExceptionTypes()));
   * Returns an instance of T, constructed using this constructor, with the
   * supplied arguments.
  public T newInstance(Object[] args) throws Throwable {
    try {
      return constructor.newInstance(args);
    } catch (InvocationTargetException e) {
      throw e.getCause();
  public String toString() {
    return constructor.toString();

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