cancel repeating task from within task spigot code example
Example: spigot cancel repeating task
int taskID;
public void startCountdown(){
taskID = Bukkit.getServer().getScheduler().scheduleSyncRepeatingTask(this,new Countdown(),20L,20L);
}
public void stopCountdown(){
Bukkit.getServer().getScheduler().cancelTask(taskID);
}
// 20L = 1 Second