======= Command Exceptions =======

Brigadier supports command exceptions which can be used to end a command such as if an argument didn't parse properly or the command failed to execute, as well as including richer details of the failure.

There are two type of command exceptions:
  * **''CommandSyntaxException''**: provided by Brigadier. It should have an exception type, and created through ''create(...)'' or ''createWithContext(...)''. It does not belong to ''RuntimeException'', so when thrown, it must be caught properly, or added in the method signature.
  * **''<yarn class_2164>'' (removed since 1.20.3)**: provided in Minecraft, and used in less cases. It belongs to ''RuntimeException''. You can directly create it with a ''Text'' as parameter.

The two main types of ''CommandSyntaxException'' are dynamic and simple exception types, of which you can call ''create()'' to create the exception to throw it. These exceptions also allow you to specify the context in which the exception was thrown using ''createWithContext(ImmutableStringReader)'', which builds the error message to point to where on the inputted command line the error occured.

Below is a coin flip command to show an example of exceptions in use.

===== Using CommandException =====
<code java [enable_line_numbers="true"]>
dispatcher.register(literal("coinflip")
    .executes(ctx -> {
        Random random = ctx.getSource().getWorld().getRandom();
			
        if(random.nextBoolean()) { // If heads succeed.
            ctx.getSource().sendFeedback(() -> Text.translatable("coin.flip.heads"), true);
            return Command.SINGLE_SUCCESS;
        }

        throw new CommandException(Text.translatable("coin.flip.tails")); 
    }));
</code>
:!: ''CommandException'' is removed since 1.20.3.

===== Using CommandSyntaxException =====

If you use ''CommandSyntaxException'', you should add a ''SimpleCommandExceptionType'' first. It is usually stored as fields, so this example presents the whole class.

<code java>
public class ExampleMod implements ModInitializer {
  public static final SimpleCommandExceptionType COIN_FLIP_TAILS = new SimpleCommandExceptionType(Text.translatable("coin.flip.tails"));
  @Override
  public void onInitialize() {
    CommandRegistrationCallback.EVENT.register((dispatcher, registryAccess, environment) -> dispatcher.register(literal("coinflip")
        .executes(ctx -> {
          Random random = ctx.getSource().getWorld().getRandom();

          if (random.nextBoolean()) { // If heads succeed.
            ctx.getSource().sendFeedback(() -> Text.translatable("coin.flip.heads"), true);
            return Command.SINGLE_SUCCESS;
          }

          throw COIN_FLIP_TAILS.create();
        })));
  }
}
</code>

Sometimes you may use ''DynamicCommandExceptionType'' to accept complex exceptions. For example:
<code java>
public class ExampleMod implements ModInitializer {
  public static final DynamicCommandExceptionType COIN_FLIP_TAILS = new DynamicCommandExceptionType(o -> Text.translatable("coin.flip.tails", o));

  @Override
  public void onInitialize() {
    CommandRegistrationCallback.EVENT.register((dispatcher, registryAccess, environment) -> dispatcher.register(literal("coinflip")
        .executes(ctx -> {
          Random random = ctx.getSource().getWorld().getRandom();

          if (random.nextBoolean()) { // If heads succeed.
            ctx.getSource().sendFeedback(() -> Text.translatable("coin.flip.heads"), true);
            return Command.SINGLE_SUCCESS;
          }

          throw COIN_FLIP_TAILS.create(ctx.getSource().getDisplayName());
        })));
  }
}
</code>

There are more Dynamic exception types which each take a different amount of arguments into account (''Dynamic2CommandExceptionType'', ''Dynamic3CommandExceptionType'', ''Dynamic4CommandExceptionType'', ''DynamicNCommandExceptionType''). You should remember that the Dynamic exceptions takes an object as an argument so you may have to cast the argument for your use.

There are some vanilla exceptions. Some can be found in ''CommandSyntaxException.BUILT_IN_EXCEPTIONS.//<exception type>//()''.