Very simple implementation of a Lua table in Java, not meant as a datastructure for using in Java programs, but as an export format.

LuaTable.java

/**
 * SIMPLE Java implementation of Lua tables
 * Mainly meant as an export format
 *
 * @author https://github.com/MasonGulu
 */

/**
 * MIT License
 *
 * Copyright (c) 2022 Mason Gulu
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

import java.util.HashMap;
import java.util.Map;

public class LuaTable {
    private final Map<Object, Object> table = new HashMap<>();
    private int lastKey = 0;
    private int lastKeySerialize = 0;

    /**
     * Put a value at a specific index
     * @param key any key
     * @param value any value
     */
    public <KT, VT> void put(KT key, VT value) {
        table.put(key, value);
    }

    /**
     * Put a value at the next sequential integer index
     * @param value any value
     */
    public <VT> void put(VT value) {
        table.put(++lastKey, value);
    }

    /**
     * Get a value from a specific index
     * @param key any key
     * @return value
     */
    public <KT> Object get(KT key) {;
        return table.get(key);
    }

    private String getLuaRep(Object obj, boolean isKey) {
        if (obj instanceof String) {
            return "\""+obj+"\"";
        } else if (obj instanceof Integer o) {
            if (o == lastKeySerialize+1 && isKey) {
                lastKeySerialize++;
                return null;
            }
            return o.toString();
        }
        return obj.toString();
    }

    /**
     * Equivalent to calling textutils.serialize on a Lua table in ComputerCraft
     *
     * @return String
     */
    public String toString() {
        // Iterate over each element in the hash map, building a string
        StringBuilder str = new StringBuilder();
        str.append("{");
        lastKeySerialize = 0;
        for (Map.Entry<Object, Object> entry : table.entrySet()) {
            Object key = entry.getKey();
            Object value = entry.getValue();
            String keyStr = getLuaRep(key, true);
            if (keyStr != null) {
                str.append("[").append(keyStr).append("]=");
            }
            str.append(getLuaRep(value, false)).append(",");
        }
        str.append("}");
        return str.toString();
    }
}