AnimatedTab.java

package me.elcorporation.animatedtab;

import net.minecraft.network.chat.ChatComponentText;
import net.minecraft.network.protocol.game.PacketPlayOutPlayerListHeaderFooter;
import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.craftbukkit.v1_17_R1.entity.CraftPlayer;
import org.bukkit.entity.Player;

import java.lang.reflect.Field;
import java.util.List;
import java.util.ArrayList;

public class TabManager {

    private List<ChatComponentText> headers = new ArrayList<>();
    private List<ChatComponentText> footers = new ArrayList<>();
    private AnimatedTab plugin;
    public TabManager(AnimatedTab plugin) {
        this.plugin = plugin;
    }

    public void showTab() {
        if (headers.isEmpty() && footers.isEmpty())
            return;
        Bukkit.getScheduler().scheduleSyncRepeatingTask(plugin, new Runnable() {
            PacketPlayOutPlayerListHeaderFooter packet = new PacketPlayOutPlayerListHeaderFooter();
            int count1 = 0; // Headers
            int count2 = 0; // Footers

            @Override
            public void run() {
                try {

                    Field a = packet.getClass().getDeclaredField("header");
                    a.setAccessible(true);
                    Field b = packet.getClass().getDeclaredField("footer");
                    b.setAccessible(true);

                    if (count1 >= headers.size())
                        count1 = 0;
                    if (count2 >= footers.size())
                        count2 = 0;
                    a.set(packet, headers.get(count1));
                    b.set(packet, footers.get(count2));

                    if (Bukkit.getOnlinePlayers().size() != 0) {
                        for (Player player : Bukkit.getOnlinePlayers())
                            ((CraftPlayer)player).getHandle().b.sendPacket(packet);

                    }

                    count1++;
                    count2++;

                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }, 10, 40);
    }
    public void addHeader(String header) {
        headers.add(new ChatComponentText(format(header)));
    }
    public void addFooter(String footer) {
        footers.add(new ChatComponentText(format(footer)));
    }
    private String format(String msg) {
        return ChatColor.translateAlternateColorCodes('&', msg);
    }
 }