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.design;
  
  import java.util.Objects;
  
  import com.puppycrawl.tools.checkstyle.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  
  /**
   * <p>
   * Restricts throws statements to a specified count.
   * Methods with "Override" or "java.lang.Override" annotation are skipped
   * from validation as current class cannot change signature of these methods.
   * </p>
   * <p>
   * Rationale:
   * Exceptions form part of a method's interface. Declaring
   * a method to throw too many differently rooted
   * exceptions makes exception handling onerous and leads
   * to poor programming practices such as writing code like
   * {@code catch(Exception ex)}. 4 is the empirical value which is based
   * on reports that we had for the ThrowsCountCheck over big projects
   * such as OpenJDK. This check also forces developers to put exceptions
   * into a hierarchy such that in the simplest
   * case, only one type of exception need be checked for by
   * a caller but any subclasses can be caught
   * specifically if necessary. For more information on rules
   * for the exceptions and their issues, see Effective Java:
   * Programming Language Guide Second Edition
   * by Joshua Bloch pages 264-273.
   * </p>
   * <p>
   * <b>ignorePrivateMethods</b> - allows to skip private methods as they do
   * not cause problems for other classes.
   * </p>
   * <ul>
   * <li>
   * Property {@code max} - Specify maximum allowed number of throws statements.
   * Type is {@code int}.
   * Default value is {@code 4}.
   * </li>
   * <li>
   * Property {@code ignorePrivateMethods} - Allow private methods to be ignored.
   * Type is {@code boolean}.
   * Default value is {@code true}.
   * </li>
   * </ul>
   * <p>
   * To configure check:
   * </p>
   * <pre>
   * &lt;module name="ThrowsCount"/&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * class Test {
   *     public void myFunction() throws CloneNotSupportedException,
   *                             ArrayIndexOutOfBoundsException,
   *                             StringIndexOutOfBoundsException,
   *                             IllegalStateException,
   *                             NullPointerException { // violation, max allowed is 4
   *         // body
   *     }
   *
   *     public void myFunc() throws ArithmeticException,
   *             NumberFormatException { // ok
   *         // body
   *     }
   *
   *     private void privateFunc() throws CloneNotSupportedException,
   *                             ClassNotFoundException,
   *                             IllegalAccessException,
   *                             ArithmeticException,
   *                             ClassCastException { // ok, private methods are ignored
   *         // body
   *     }
   *
   * }
   * </pre>
   * <p>
   * To configure the check so that it doesn't allow more than two throws per method:
   * </p>
   * <pre>
   * &lt;module name="ThrowsCount"&gt;
   *   &lt;property name=&quot;max&quot; value=&quot;2&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * class Test {
   *     public void myFunction() throws IllegalStateException,
   *                                 ArrayIndexOutOfBoundsException,
   *                                 NullPointerException { // violation, max allowed is 2
   *         // body
   *     }
   *
   *     public void myFunc() throws ArithmeticException,
   *                                 NumberFormatException { // ok
   *         // body
   *     }
   *
   *     private void privateFunc() throws CloneNotSupportedException,
   *                                 ClassNotFoundException,
   *                                 IllegalAccessException,
   *                                 ArithmeticException,
   *                                 ClassCastException { // ok, private methods are ignored
   *         // body
   *     }
   *
   * }
   * </pre>
   * <p>
   * To configure the check so that it doesn't skip private methods:
   * </p>
   * <pre>
   * &lt;module name="ThrowsCount"&gt;
   *   &lt;property name=&quot;ignorePrivateMethods&quot; value=&quot;false&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * class Test {
   *     public void myFunction() throws CloneNotSupportedException,
   *                                 ArrayIndexOutOfBoundsException,
   *                                 StringIndexOutOfBoundsException,
   *                                 IllegalStateException,
   *                                 NullPointerException { // violation, max allowed is 4
   *         // body
   *     }
   *
   *     public void myFunc() throws ArithmeticException,
   *                                 NumberFormatException { // ok
   *         // body
   *     }
   *
   *     private void privateFunc() throws CloneNotSupportedException,
   *                                 ClassNotFoundException,
   *                                 IllegalAccessException,
   *                                 ArithmeticException,
   *                                 ClassCastException { // violation, max allowed is 4
   *         // body
   *     }
   *
   *     private void func() throws IllegalStateException,
   *                                 NullPointerException { // ok
   *         // body
   *     }
   *
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code throws.count}
   * </li>
   * </ul>
   *
   * @since 3.2
   */
  @StatelessCheck
  public final class ThrowsCountCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "throws.count";
  
      /** Default value of max property. */
      private static final int DEFAULT_MAX = 4;
  
      /** Allow private methods to be ignored. */
      private boolean ignorePrivateMethods = true;
  
      /** Specify maximum allowed number of throws statements. */
      private int max;
  
      /** Creates new instance of the check. */
      public ThrowsCountCheck() {
          max = DEFAULT_MAX;
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {
              TokenTypes.LITERAL_THROWS,
          };
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      /**
       * Setter to allow private methods to be ignored.
       *
       * @param ignorePrivateMethods whether private methods must be ignored.
       */
      public void setIgnorePrivateMethods(boolean ignorePrivateMethods) {
          this.ignorePrivateMethods = ignorePrivateMethods;
      }
  
      /**
       * Setter to specify maximum allowed number of throws statements.
       *
       * @param max maximum allowed throws statements.
       */
      public void setMax(int max) {
          this.max = max;
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          if (ast.getType() == TokenTypes.LITERAL_THROWS) {
              visitLiteralThrows(ast);
          }
          else {
              throw new IllegalStateException(ast.toString());
          }
      }
  
      /**
       * Checks number of throws statements.
       *
       * @param ast throws for check.
       */
      private void visitLiteralThrows(DetailAST ast) {
          if ((!ignorePrivateMethods || !isInPrivateMethod(ast))
                  && !isOverriding(ast)) {
              // Account for all the commas!
              final int count = (ast.getChildCount() + 1) / 2;
              if (count > max) {
                  log(ast, MSG_KEY, count, max);
              }
          }
      }
  
      /**
       * Check if a method has annotation @Override.
       *
       * @param ast throws, which is being checked.
       * @return true, if a method has annotation @Override.
       */
      private static boolean isOverriding(DetailAST ast) {
          final DetailAST modifiers = ast.getParent().findFirstToken(TokenTypes.MODIFIERS);
          boolean isOverriding = false;
          DetailAST child = modifiers.getFirstChild();
          while (child != null) {
              if (child.getType() == TokenTypes.ANNOTATION
                      && "Override".equals(getAnnotationName(child))) {
                  isOverriding = true;
                  break;
              }
              child = child.getNextSibling();
          }
          return isOverriding;
      }
  
      /**
       * Gets name of an annotation.
       *
       * @param annotation to get name of.
       * @return name of an annotation.
       */
      private static String getAnnotationName(DetailAST annotation) {
          final DetailAST dotAst = annotation.findFirstToken(TokenTypes.DOT);
          final DetailAST parent = Objects.requireNonNullElse(dotAst, annotation);
          return parent.findFirstToken(TokenTypes.IDENT).getText();
      }
  
      /**
       * Checks if method, which throws an exception is private.
       *
       * @param ast throws, which is being checked.
       * @return true, if method, which throws an exception is private.
       */
      private static boolean isInPrivateMethod(DetailAST ast) {
          final DetailAST methodModifiers = ast.getParent().findFirstToken(TokenTypes.MODIFIERS);
          return methodModifiers.findFirstToken(TokenTypes.LITERAL_PRIVATE) != null;
      }
  
  }
  