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Java example source code file (InternalContext.java)

This example Java source code file (InternalContext.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

constructioncontext, dependency, dependencyandsource, dependencystack, injectoroptions, internalcontext, key, list, map, object, suppresswarnings, util

The InternalContext.java Java example source code

 * Copyright (C) 2006 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.internal;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.inject.Key;
import com.google.inject.internal.InjectorImpl.InjectorOptions;
import com.google.inject.spi.Dependency;
import com.google.inject.spi.DependencyAndSource;

import java.util.Arrays;
import java.util.List;
import java.util.Map;

 * Internal context. Used to coordinate injections and support circular
 * dependencies.
 * @author crazybob@google.com (Bob Lee)
final class InternalContext {

  private final InjectorOptions options;

  private Map<Object, ConstructionContext constructionContexts = Maps.newHashMap();

  /** Keeps track of the type that is currently being requested for injection. */
  private Dependency<?> dependency;

  /** Keeps track of the hierarchy of types needed during injection. */
  private final DependencyStack state = new DependencyStack();

  InternalContext(InjectorOptions options) {
    this.options = options;

  public InjectorOptions getInjectorOptions() {
    return options;

  public <T> ConstructionContext getConstructionContext(Object key) {
    ConstructionContext<T> constructionContext
        = (ConstructionContext<T>) constructionContexts.get(key);
    if (constructionContext == null) {
      constructionContext = new ConstructionContext<T>();
      constructionContexts.put(key, constructionContext);
    return constructionContext;

  public Dependency<?> getDependency() {
    return dependency;

  /** Sets the new current dependency & adds it to the state. */
  public Dependency<?> pushDependency(Dependency dependency, Object source) {
    Dependency<?> previous = this.dependency;
    this.dependency = dependency;
    state.add(dependency, source);
    return previous;

  /** Pops the current state & sets the new dependency. */
  public void popStateAndSetDependency(Dependency<?> newDependency) {
    this.dependency = newDependency;

  /** Adds to the state without setting the dependency. */
  public void pushState(Key<?> key, Object source) {
    state.add(key, source);
  /** Pops from the state without setting a dependency. */
  public void popState() {

  /** Returns the current dependency chain (all the state). */
  public List<DependencyAndSource> getDependencyChain() {
    ImmutableList.Builder<DependencyAndSource> builder = ImmutableList.builder();
    for (int i = 0; i < state.size(); i += 2) {
      Object evenEntry = state.get(i);
      Dependency<?> dependency;
      if (evenEntry instanceof Key) {
        dependency = Dependency.get((Key<?>) evenEntry);
      } else {
        dependency = (Dependency<?>) evenEntry;
      builder.add(new DependencyAndSource(dependency, state.get(i + 1)));
    return builder.build();

   * Keeps track of the hierarchy of types needed during injection.
   * <p>This is a pairwise combination of dependencies and sources, with dependencies or keys on
   * even indices, and sources on odd indices. This structure is to avoid the memory overhead of
   * DependencyAndSource objects, which can add to several tens of megabytes in large applications.
  private static final class DependencyStack {
    private Object[] elements = new Object[16];
    private int size = 0;

    public void add(Object dependencyOrKey, Object source) {
      if (elements.length < size + 2) {
        elements = Arrays.copyOf(elements, (elements.length*3)/2 + 2);
      elements[size++] = dependencyOrKey;
      elements[size++] = source;

    public void pop() {
      elements[--size] = null;
      elements[--size] = null;

    public Object get(int i) {
      return elements[i];

    public int size() {
      return size;

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