content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to you 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,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.calcite.util;
  
  import java.io.StringWriter;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  /**
   * Contains methods that call JDK methods that the
   * <a href="https://github.com/policeman-tools/forbidden-apis">forbidden
   * APIs checker</a> does not approve of.
   *
   * <p>This class is excluded from the check, so methods called via this class
   * will not fail the build.
   */
  public class Unsafe {
    private Unsafe() {}
  
    /** Calls {@link System#exit}. */
    public static void systemExit(int status) {
      System.exit(status);
    }
  
    /** Calls {@link Object#notifyAll()}. */
    public static void notifyAll(Object o) {
      o.notifyAll();
    }
  
    /** Calls {@link Object#wait()}. */
    @SuppressWarnings("WaitNotInLoop")
    public static void wait(Object o) throws InterruptedException {
      o.wait();
    }
  
    /** Clears the contents of a {@link StringWriter}. */
    @SuppressWarnings("JdkObsolete")
    public static void clear(StringWriter sw) {
      // Included in this class because StringBuffer is banned.
      sw.getBuffer().setLength(0);
    }
  
    /** Helper for the SQL {@code REGEXP_REPLACE} function.
     *
     * <p>It is marked "unsafe" because it uses {@link StringBuffer};
     * Versions of {@link Matcher#appendReplacement(StringBuffer, String)}
     * and {@link Matcher#appendTail(StringBuffer)}
     * that use {@link StringBuilder} are not available until JDK 9. */
    @SuppressWarnings("JdkObsolete")
    public static String regexpReplace(String s, Pattern pattern,
        String replacement, int pos, int occurrence) {
      Bug.upgrade("when we drop JDK 8, replace StringBuffer with StringBuilder");
      final StringBuffer sb = new StringBuffer();
      final String input;
      if (pos != 1) {
        sb.append(s, 0, pos - 1);
        input = s.substring(pos - 1);
      } else {
        input = s;
      }
  
      int count = 0;
      Matcher matcher = pattern.matcher(input);
      while (matcher.find()) {
        if (occurrence == 0) {
          matcher.appendReplacement(sb, replacement);
        } else if (++count == occurrence) {
          matcher.appendReplacement(sb, replacement);
          break;
        }
      }
      matcher.appendTail(sb);
  
      return sb.toString();
    }
  }
  