freemarker-generator-base/src/main/java/org/apache/freemarker/generator/base/util/ListUtils.java

/*
 * 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.freemarker.generator.base.util;

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

public class ListUtils {

    public static <T> boolean isNullOrEmpty(final List<T> list) {
        return list == null || list.isEmpty();
    }

    /**
     * Transposes the given tabular data, swapping rows with columns.
     *
     * @param <T>   the type of the table
     * @param table the table
     * @return the transposed table
     * @throws NullPointerException if the given table is {@code null}
     */
    public static <T> List<List<T>> transpose(final List<List<T>> table) {
        if (isNullOrEmpty(table)) {
            return new ArrayList<>();
        }

        final List<List<T>> result = new ArrayList<>();
        for (int i = 0; i < table.get(0).size(); i++) {
            final List<T> col = new ArrayList<>();
            for (List<T> row : table) {
                col.add(row.get(i));
            }
            result.add(col);
        }
        return result;
    }

    /**
     * Returns the first non-null value of the list.
     *
     * @param list array
     * @param <T>  the type of the array
     * @return copied array
     */
    public static <T> T coalesce(List<T> list) {
        return list.stream().filter(Objects::nonNull).findFirst().orElseGet(() -> null);
    }

    /**
     * Copy an array to another array while casting to <code>R</code>.
     *
     * @param array array to copy
     * @param <T>   the source type of the array
     * @param <R>   the target type of the array
     * @return copied array
     */
    @SuppressWarnings("unchecked")
    public static <T, R> List<R> copy(final List<T> array) {
        final List<R> result = new ArrayList<>();
        for (int i = 0; i < array.size(); i++) {
            result.set(i, (R) array.get(i));
        }
        return result;
    }
}