code: ///////////////////////////////////////////////////////////////////////////////////////////////
  // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
  // Copyright (C) 2001-2023 the original author or authors.
  //
  // This library is free software; you can redistribute it and/or
  // modify it under the terms of the GNU Lesser General Public
  // License as published by the Free Software Foundation; either
  // version 2.1 of the License, or (at your option) any later version.
  //
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  // Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public
  // License along with this library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle.checks.regexp;
  
  import java.io.File;
  
  import com.puppycrawl.tools.checkstyle.PropertyType;
  import com.puppycrawl.tools.checkstyle.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.XdocsPropertyType;
  import com.puppycrawl.tools.checkstyle.api.AbstractFileSetCheck;
  import com.puppycrawl.tools.checkstyle.api.FileText;
  
  /**
   * <p>
   * Checks that a specified pattern matches a single-line in any file type.
   * </p>
   * <p>
   * Rationale: This check can be used to prototype checks and to find common bad
   * practice such as calling {@code ex.printStacktrace()},
   * {@code System.out.println()}, {@code System.exit()}, etc.
   * </p>
   * <ul>
   * <li>
   * Property {@code format} - Specify the format of the regular expression to match.
   * Type is {@code java.util.regex.Pattern}.
   * Default value is {@code "$."}.
   * </li>
   * <li>
   * Property {@code message} - Specify the message which is used to notify about
   * violations, if empty then default (hard-coded) message is used.
   * Type is {@code java.lang.String}.
   * Default value is {@code null}.
   * </li>
   * <li>
   * Property {@code ignoreCase} - Control whether to ignore case when searching.
   * Type is {@code boolean}.
   * Default value is {@code false}.
   * </li>
   * <li>
   * Property {@code minimum} - Specify the minimum number of matches required in each file.
   * Type is {@code int}.
   * Default value is {@code 0}.
   * </li>
   * <li>
   * Property {@code maximum} - Specify the maximum number of matches required in each file.
   * Type is {@code int}.
   * Default value is {@code 0}.
   * </li>
   * <li>
   * Property {@code fileExtensions} - Specify the file type extension of files to process.
   * Type is {@code java.lang.String[]}.
   * Default value is {@code ""}.
   * </li>
   * </ul>
   * <p>
   *   To configure the default check:
   * </p>
   * <pre>
   * &lt;module name="RegexpSingleline" /&gt;
   * </pre>
   * <p>
   *   This configuration does not match to anything,
   *   so we do not provide any code example for it
   *   as no violation will ever be reported.
   * </p>
   * <p>
   * To configure the check to find occurrences of 'System.exit('
   * with some <i>slack</i> of allowing only one occurrence per file:
   * </p>
   * <pre>
   * &lt;module name="RegexpSingleline"&gt;
   *   &lt;property name="format" value="System.exit\("/&gt;
   *   &lt;!-- next line not required as 0 is the default --&gt;
   *   &lt;property name="minimum" value="0"/&gt;
   *   &lt;property name="maximum" value="1"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * class MyClass {
   *      void myFunction() {
   *          try {
   *             doSomething();
   *          } catch (Exception e) {
   *             System.exit(1); // OK, as only there is only one occurrence.
   *          }
   *      }
   *      void doSomething(){};
   * }
   * </pre>
   * <pre>
   * class MyClass {
   *     void myFunction() {
   *         try {
   *             doSomething();
   *             System.exit(0);
   *         } catch (Exception e) {
   *             System.exit(1); // Violation, as there are more than one occurrence.
   *         }
   *     }
   *     void doSomething(){};
   * }
   * </pre>
   * <p>
   * An example of how to configure the check to make sure a copyright statement
   * is included in the file:
   * </p>
   * <pre>
   * &lt;module name="RegexpSingleline"&gt;
   *   &lt;property name="format" value="This file is copyrighted"/&gt;
   *   &lt;property name="minimum" value="1"/&gt;
   *   &lt;!--  Need to specify a maximum, so 10 times is more than enough. --&gt;
   *   &lt;property name="maximum" value="10"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * &#47;**
   * * This file is copyrighted under CC. // Ok, as the file contains a copyright statement.
   * *&#47;
   * class MyClass {
   *
   * }
   * </pre>
   * <pre>
   * &#47;** // violation, as the file doesn't contain a copyright statement.
   * * MyClass as a configuration example.
   * *&#47;
   * class MyClass {
   *
   * }
   * </pre>
   * <p>
   *  An example of how to configure the check to make sure sql files contains the term 'license'.
   * </p>
   * <pre>
   * &lt;module name="RegexpSingleline"&gt;
   *     &lt;property name="format" value="license"/&gt;
   *     &lt;property name="minimum" value="1"/&gt;
   *     &lt;property name="maximum" value="9999"/&gt;
   *     &lt;property name="ignoreCase" value="true"/&gt;
   *     &lt;!--  Configure a message to be shown on violation of the Check. --&gt;
   *     &lt;property name="message"
   *           value="File must contain at least one occurrence of 'license' term"/&gt;
  *      &lt;!--  Perform the Check only on files with java extension. --&gt;
   *     &lt;property name="fileExtensions" value="sql"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * &#47;*
   * AP 2.0 License. // Ok, Check ignores the case of the term.
   * *&#47;
   * CREATE DATABASE MyDB;
   * </pre>
   * <pre>
   * &#47;* // violation, file doesn't contain the term.
   * Example sql file.
   * *&#47;
   * CREATE DATABASE MyDB;
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.Checker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code regexp.exceeded}
   * </li>
   * <li>
   * {@code regexp.minimum}
   * </li>
   * </ul>
   *
   * @since 5.0
   */
  @StatelessCheck
  public class RegexpSinglelineCheck extends AbstractFileSetCheck {
  
      /** Specify the format of the regular expression to match. */
      @XdocsPropertyType(PropertyType.PATTERN)
      private String format = "$.";
      /**
       * Specify the message which is used to notify about violations,
       * if empty then default (hard-coded) message is used.
       */
      private String message;
      /** Specify the minimum number of matches required in each file. */
      private int minimum;
      /** Specify the maximum number of matches required in each file. */
      private int maximum;
      /** Control whether to ignore case when searching. */
      private boolean ignoreCase;
  
      /** The detector to use. */
      private SinglelineDetector detector;
  
      @Override
      public void beginProcessing(String charset) {
          final DetectorOptions options = DetectorOptions.newBuilder()
              .reporter(this)
              .format(format)
              .message(message)
              .minimum(minimum)
              .maximum(maximum)
              .ignoreCase(ignoreCase)
              .build();
          detector = new SinglelineDetector(options);
      }
  
      @Override
      protected void processFiltered(File file, FileText fileText) {
          detector.processLines(fileText);
      }
  
      /**
       * Setter to specify the format of the regular expression to match.
       *
       * @param format the format of the regular expression to match.
       */
      public void setFormat(String format) {
          this.format = format;
      }
  
      /**
       * Setter to specify the message which is used to notify about violations,
       * if empty then default (hard-coded) message is used.
       *
       * @param message the message to report for a match.
       */
      public void setMessage(String message) {
          this.message = message;
      }
  
      /**
       * Setter to specify the minimum number of matches required in each file.
       *
       * @param minimum the minimum number of matches required in each file.
       */
      public void setMinimum(int minimum) {
          this.minimum = minimum;
      }
  
      /**
       * Setter to specify the maximum number of matches required in each file.
       *
       * @param maximum the maximum number of matches required in each file.
       */
      public void setMaximum(int maximum) {
          this.maximum = maximum;
      }
  
      /**
       * Setter to control whether to ignore case when searching.
       *
       * @param ignoreCase whether to ignore case when searching.
       */
      public void setIgnoreCase(boolean ignoreCase) {
          this.ignoreCase = ignoreCase;
      }
  
  }
  