Example - Username color changing plugin

Say we want to create a plugin to change the color of a player's username. We want to create a command of the following form:

/namecolor <chatcolor>

We then use the ChatColorArgument to change the player's name color:

LinkedHashMap<String, Argument> arguments = new LinkedHashMap<>();
arguments.put("chatcolor", new ChatColorArgument());

new CommandAPICommand("namecolor")
    .withArguments(arguments)
    .executesPlayer((player, args) -> {
        ChatColor color = (ChatColor) args[0];
	    player.setDisplayName(color + player.getName());
    })
    .register();

Example - Book made from raw JSON

Say we want to generate a book using raw JSON. For this example, we'll use the following JSON (generated from minecraftjson.com) to generate our book:

["", {
    "text": "Once upon a time, there was a guy call "
}, {
    "text": "Skepter",
    "color": "light_purple",
    "hoverEvent": {
        "action": "show_entity",
        "value": "Skepter"
    }
}, {
    "text": " and he created the "
}, {
    "text": "CommandAPI",
    "underlined": true,
    "clickEvent": {
        "action": "open_url",
        "value": "https://github.com/JorelAli/1.13-Command-API"
    }
}]

Since we're writing a book, we must ensure that all quotes have been escaped. This can also be performed on the minecraftjson.com website by selecting "book":

["[\"\",{\"text\":\"Once upon a time, there was a guy call \"},{\"text\":\"Skepter\",\"color\":\"light_purple\",\"hoverEvent\":{\"action\":\"show_entity\",\"value\":\"Skepter\"}},{\"text\":\" and he created the \"},{\"text\":\"CommandAPI\",\"underlined\":true,\"clickEvent\":{\"action\":\"open_url\",\"value\":\"https://github.com/JorelAli/1.13-Command-API\"}}]"]

Now let's define our command. Since book text is typically very large - too large to be entered into a chat, we'll make a command block compatible command by providing a player parameter:

/makebook <player> <contents>

Now we can create our book command. We use the player as the main target by using their name for the author field, as well as their inventory to place the book. We finally construct our book using the .setPages(BaseComponent[]) method:

LinkedHashMap<String, Argument> arguments = new LinkedHashMap<>();
arguments.put("player", new PlayerArgument());
arguments.put("contents", new ChatComponentArgument());

new CommandAPICommand("makebook")
    .withArguments(arguments)
    .executes((sender, args) -> {
        Player player = (Player) args[0];
        BaseComponent[] arr = (BaseComponent[]) args[1];
        
        //Create book
        ItemStack is = new ItemStack(Material.WRITTEN_BOOK);
        BookMeta meta = (BookMeta) is.getItemMeta(); 
        meta.setTitle("Custom Book");
        meta.setAuthor(player.getName());
        meta.spigot().setPages(arr);
        is.setItemMeta(meta);
        
        //Give player the book
        player.getInventory().addItem(is);
    })
    .register();

Example - Sending personalized messages to players

Say we wanted to broadcast a "personalized" message to players on the server. By "personalized", we mean a command which changes its output depending on who we are sending the output to. Simply put, we want a command of the following structure:

/pbroadcast <message>

Say we're on a server with 2 players: Bob and Michael. If I were to use the following command:

/pbroadcast Hello @p

Bob would receive the message "Hello Bob", whereas Michael would receive the message "Hello Michael". We can use the ChatArgument to create this "personalized" broadcast:

LinkedHashMap<String, Argument> arguments = new LinkedHashMap<>();
arguments.put("message", new ChatArgument());

new CommandAPICommand("pbroadcast")
    .withArguments(arguments)
    .executes((sender, args) -> {
        BaseComponent[] message = (BaseComponent[]) args[0];
    
        //Broadcast the message to everyone on the server
        Bukkit.getServer().spigot().broadcast(message);
    })
    .register();