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Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more.

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/*
 * Copyright (C) 2009 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.io;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.IOException;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A callback to be used with the streaming {@code readLines} methods.
 *
 * {@link #processLine} will be called for each line that is read, and should return {@code
 * false} when you want to stop processing.
 *
 * @author Miles Barr
 * @since 1.0
 */
@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public interface LineProcessor {

  /**
   * This method will be called once for each line.
   *
   * @param line the line read from the input, without delimiter
   * @return true to continue processing, false to stop
   */
  @CanIgnoreReturnValue // some uses know that their processor never returns false
  boolean processLine(String line) throws IOException;

  /** Return the result of processing all the lines. */
  @ParametricNullness
  T getResult();
}