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Java example source code file (

This example Java source code file ( is included in the "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

assertionerror, class, default_instance, immutableset, iterable, list, object, sourceprovider, stacktraceelement, string, the, unknown_source, util

The 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
 * 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.



import java.util.List;

 * Provides access to the calling line of code.
 * @author (Bob Lee)
public final class SourceProvider {

  /** Indicates that the source is unknown. */
  public static final Object UNKNOWN_SOURCE = "[unknown source]";

  private final SourceProvider parent;
  private final ImmutableSet<String> classNamesToSkip;
  public static final SourceProvider DEFAULT_INSTANCE
      = new SourceProvider(ImmutableSet.of(SourceProvider.class.getName()));

  private SourceProvider(Iterable<String> classesToSkip) {
    this(null, classesToSkip);

  private SourceProvider(SourceProvider parent, Iterable<String> classesToSkip) {
    this.parent = parent;
    ImmutableSet.Builder<String> classNamesToSkipBuilder = ImmutableSet.builder();
    for (String classToSkip : classesToSkip) {
      if (parent == null || !parent.shouldBeSkipped(classToSkip)) {
    this.classNamesToSkip =;

  /** Returns a new instance that also skips {@code moreClassesToSkip}. */
  public SourceProvider plusSkippedClasses(Class... moreClassesToSkip) {
    return new SourceProvider(this, asStrings(moreClassesToSkip));

  /** Returns true if the className should be skipped. */
  private boolean shouldBeSkipped(String className) {
    return (parent != null && parent.shouldBeSkipped(className))
        || classNamesToSkip.contains(className);
  /** Returns the class names as Strings */
  private static List<String> asStrings(Class... classes) {
    List<String> strings = Lists.newArrayList();
    for (Class c : classes) {
    return strings;

   * Returns the calling line of code. The selected line is the nearest to the top of the stack that
   * is not skipped.
  public StackTraceElement get(StackTraceElement[] stackTraceElements) {
    Preconditions.checkNotNull(stackTraceElements, "The stack trace elements cannot be null.");
    for (final StackTraceElement element : stackTraceElements) {
      String className = element.getClassName();
      if (!shouldBeSkipped(className)) {
        return element;
    throw new AssertionError();

   * Returns the non-skipped module class name.
  public Object getFromClassNames(List<String> moduleClassNames) {
    Preconditions.checkNotNull(moduleClassNames, "The list of module class names cannot be null.");
    for (final String moduleClassName : moduleClassNames) {
      if (!shouldBeSkipped(moduleClassName)) {
        return new StackTraceElement(moduleClassName, "configure", null, -1);
    return UNKNOWN_SOURCE;

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