Components

Components (base interface Component) are forms of text used by Minecraft and Forge to concisely hold data relating to text. They form the basis of the chat system used in Minecraft. They are used for serializing and sending text data over network to players, displaying on clients, and styling for how the text appears with modifiers like bold and coloration.

There are two main types of components: TextComponents and TranslatableComponents. Both serve different purposes, although you should prefer the latter one for most general mod development. Both of these also extend from a base class of BaseComponent, which has some important properties.

BaseComponent

Components at their most basic level hold a Style object and a list of "sibling" components named siblings. In reality, these "siblings" are actually children of the main component, and are treated as such when formatting with the Style object. A style can be applied to a component by calling withStyle and setStyle. withStyle modifies the existing Style object with the given property, while setStyle replaces the current Style object. By default, components use a style of Style.EMPTY, with an empty color representing white and empty properties meaning no special chat formatting. To add a light blue color for example, one could simple call theBaseComponent.withStyle(ChatFormatting.BLUE). This will merge the BLUE color with the existing Style object. When applying a parent component's Style to its children components, a non-null property of a child Style will take precedence over its parent Style. This means that if the color is set for both a child and parent component, the child's color will be displayed. Otherwise, non-null properties from a parent component's Style override properties from the child Style if they are null.

Appending siblings

Siblings can be appended to components similar to the plus (+) operator with Strings via BaseComponent#append(Component).

TextComponent

Text components are the most basic form of components. They are raw components that contain a single String object. These are not preferred for general mod development as they cannot be translated into other languages. All properties of the base BaseComponent apply to text components.

Creating

Text components are instantiated in the form new TextComponent("Hello, world!"). In practice, when sent to a player, this would simply be displayed as declared: Hello, world!.

Usage

Text components are most commonly used to create empty or space-filling components, which can then link multiple components together using appendSibling.

TranslatableComponent

Translatable components are a more advanced form of components that support String formatting and translation into multiple languages. Translatable components hold a translation key, which is integral to translation into other languages. Translation keys are then mapped with a language file (commonly know as a lang file) to their appropriate entry for each translated language. It is important to note that the translation key is translated by the client, not the server. The server sends the translation key to the player, and the player's client converts the translation key into its fully expanded form when rendering depending on the player's selected language. If a player selects a specific language for which a translation key is not mapped, it will default to English.

Format modifiers

Translatable components also support format modifiers like used in String#format. These format modifiers are declared by using the string %s when creating a translation entry for a given translation key. This format modifier will then be expanded and replaced with the provided object when rendered by the client. Any other format modifiers like %d or %n are not supported and will throw a formatting error. To get a normal percentage, a double percentage sign must be used (%%). A number can also be inserted, and it will be used as a 1-based index to select the argument. This is useful for choosing a specific argument out of order, or using the same argument twice. This looks like %1$s. The list of arguments to expand these format modifiers are passed to the constructor of the TranslatableComponent using an Object varargs parameter, similar to String#format. The arguments passed in the constructor of a TranslatableComponent can be either an Object or another Component. Any Components will be expanded and have any declared Styles properties preserved in the final output. Any objects that are not an instance of Component will have Object#toString called during expansion.

Creating

Translatable components are instantiated in the form new TranslatableComponent("your.translation_key.here", new TextComponent("thing1").withStyle(ChatFormatting.RED), new TextComponent("thing2").withStyle(ChatFormatting.BLUE)). In your lang file, the entry would look something like:

{
    "your.translation_key.here": "I like using %1$s and %2$s!"
}

In practice, when sent to a player, this would be displayed as I like using thing1 and thing2!, where thing1 would be colored as red and thing2 would be colored as blue. Normal Strings can also be passed in, and they will inherit the Style object of the main component. Note that any more values in the language file must be declared as comma-separated key-value pairs as required by the JSON specification, with the last key-value pair not ending with a comment.

Usage

Translatable components are used for sending anything visual to the player. Using them provides a benefit of format modifiers and the ability to be translated into different languages. This means that, given a translator, one could translate the English translation file (by default, en_us.json) into another language for a given mod. This system is also used by Minecraft itself and has been used to translate the game into hundreds of languages. Translation keys are also required for declaring the names of items, blocks, and entities in the game.