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The DiffUtils library for computing diffs, applying patches, generationg side-by-side view in Java.

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/*-
 * #%L
 * java-diff-utils
 * %%
 * Copyright (C) 2009 - 2017 java-diff-utils
 * %%
 * 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.
 * #L%
 */
package com.github.difflib.patch;

import java.util.List;
import java.util.Objects;

/**
 * Describes the change-delta between original and revised texts.
 *
 * @author Dmitry Naumenko
 * @param T The type of the compared elements in the data 'lines'.
 */
public final class ChangeDelta extends AbstractDelta {

    /**
     * Creates a change delta with the two given chunks.
     *
     * @param source The source chunk. Must not be {@code null}.
     * @param target The target chunk. Must not be {@code null}.
     */
    public ChangeDelta(Chunk source, Chunk target) {
        super(DeltaType.CHANGE, source, target);
        Objects.requireNonNull(source, "source must not be null");
        Objects.requireNonNull(target, "target must not be null");
    }

    @Override
    public void applyTo(List target) throws PatchFailedException {
        verifyChunk(target);
        int position = getSource().getPosition();
        int size = getSource().size();
        for (int i = 0; i < size; i++) {
            target.remove(position);
        }
        int i = 0;
        for (T line : getTarget().getLines()) {
            target.add(position + i, line);
            i++;
        }
    }

    @Override
    public void restore(List target) {
        int position = getTarget().getPosition();
        int size = getTarget().size();
        for (int i = 0; i < size; i++) {
            target.remove(position);
        }
        int i = 0;
        for (T line : getSource().getLines()) {
            target.add(position + i, line);
            i++;
        }
    }

    @Override
    public String toString() {
        return "[ChangeDelta, position: " + getSource().getPosition() + ", lines: "
                + getSource().getLines() + " to " + getTarget().getLines() + "]";
    }
}