https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2016 The Guava Authors
 *
 * 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
 *
 * 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 com.google.common.base;

import com.google.common.annotations.GwtCompatible;


The subset of the Pattern API which is used by this package, and also shared with the re2j library. For internal use only. Please refer to the Pattern javadoc for details. 
/**
 * The subset of the {@link java.util.regex.Pattern} API which is used by this package, and also
 * shared with the {@code re2j} library. For internal use only. Please refer to the {@code Pattern}
 * javadoc for details.
 */
@GwtCompatible
abstract class CommonPattern {
  abstract CommonMatcher matcher(CharSequence t);

  abstract String pattern();

  abstract int flags();

  // Re-declare these as abstract to force subclasses to override.
  @Override
  public abstract String toString();

  @Override
  public abstract int hashCode();

  @Override
  public abstract boolean equals(Object o);
}