But still, it is very powerful, and allows you to declare arbitrarily deeply nested dependency "graphs" (trees).

/// tip

All this might not seem as useful with these simple examples.

But you will see how useful it is in the chapters about **security**.

And you will also see the amounts of code it will save you.

                is not available, instead of erroring out, the dependency result will
                be `None`.

                This is useful when you want to have optional authentication.

                It is also useful when you want to have authentication that can be
                provided in one of multiple optional ways (for example, with OAuth2
                or in a cookie).

                is not available, instead of erroring out, the dependency result will
                be `None`.

                This is useful when you want to have optional authentication.

                It is also useful when you want to have authentication that can be
                provided in one of multiple optional ways (for example, in HTTP Basic

package org.apache.maven.exception;

import java.util.Collections;
import java.util.List;

/**
 * Provide a summary of the exception, containing:<ul>
 * <li>the exception itself,</li>
 * <li>useful end-user message,</li>
 * <li>useful reference to a solution, or set of solutions: this is usually a wiki page url in
 * <a href="http://cwiki.apache.org/confluence/display/MAVEN/">http://cwiki.apache.org/confluence/display/MAVEN/</a>,
 * </li>

Environment variables could be useful for handling application **settings**, as part of the **installation** of Python, etc.

## Create and Use Env Vars

You can **create** and use environment variables in the **shell (terminal)**, without needing Python:

    return spec.toCacheBuilder().lenientParsing();
  }

  /**
   * Constructs a new {@code CacheBuilder} instance with the settings specified in {@code spec}.
   * This is especially useful for command-line configuration of a {@code CacheBuilder}.
   *
   * @param spec a String in the format specified by {@link CacheBuilderSpec}
   * @since 12.0
   */
  @GwtIncompatible // To be supported

package com.google.common.base;

import static java.util.concurrent.TimeUnit.NANOSECONDS;

import com.google.caliper.Benchmark;

/**
 * Simple benchmark: create, start, read. This does not currently report the most useful result
 * because it's ambiguous to what extent the stopwatch benchmark is being affected by GC.
 *
 * @author Kevin Bourrillion
 */
public class StopwatchBenchmark {
  @Benchmark
  long stopwatch(int reps) {

1. 3.2.4-alpha-1 == 3.2.4.alpha.1
   3.2.4-alpha-1 < 3.2.4-SNAPSHOT
2. 3.2.4-SNAPSHOT == 3.2.4.snapshot
   3.2.4-SNAPSHOT < 3.2.4.0
3. 3.2.4.0 == 3.2.4
+----+

* Useful entry points

 * artifact version comparison {{{./apidocs/org/apache/maven/artifact/versioning/ComparableVersion.html}javadoc}},

This is very useful when you need to:

* Have shared logic (the same code logic again and again).
* Share database connections.
* Enforce security, authentication, role requirements, etc.
* And many other things...

All these, while minimizing code repetition.

## First Steps

Let's see a very simple example. It will be so simple that it is not very useful, for now.

 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.maven.exception;

/**
 * Transform an exception into useful end-user message.
 *
 * @since 3.0-alpha-3
 */
public interface ExceptionHandler {
    ExceptionSummary handleException(Throwable e);