content: package org.apache.lucene.util.fst;
  
  /**
   * 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.
   */
  
  import java.io.IOException;
  
  import org.apache.lucene.store.DataInput;
  import org.apache.lucene.store.DataOutput;
  
  /**
   * Represents the outputs for an FST, providing the basic
   * algebra needed for the FST.
   *
   * @lucene.experimental
   */
  
  public abstract class Outputs<T> {
  
    // TODO: maybe change this API to allow for re-use of the
    // output instances -- this is an insane amount of garbage
    // (new object per byte/char/int) if eg used during
    // analysis
  
    /** Eg common("foo", "foobar") -> "foo" */
    public abstract T common(T output1, T output2);
  
    /** Eg subtract("foobar", "foo") -> "bar" */
    public abstract T subtract(T output, T inc);
  
    /** Eg add("foo", "bar") -> "foobar" */
    public abstract T add(T prefix, T output);
  
    public abstract void write(T output, DataOutput out) throws IOException;
  
    public abstract T read(DataInput in) throws IOException;
  
    /** NOTE: this output is compared with == so you must
     *  ensure that all methods return the single object if
     *  it's really no output */
    public abstract T getNoOutput();
  
    public abstract String outputToString(T output);
  
    public T merge(T first, T second) {
      throw new UnsupportedOperationException();
    }
  }
  