Commands and Subsystems

Commands

Commands are used to control the robot. They activate Subsystems when they get the proper input. The requires method makes sure that a subsystem is only accessed by 1 command at a time.

[This class] is at the very core of the entire command framework. Every command can be started with a call to start(). Once a command is started it will call initialize(), and then will repeatedly call execute() until the isFinished() returns true. Once it does, end() will be called.

Command Types

There are 4 types of commands: InstantCommand, CommandGroup, TimedCommand, and Command.

InstantCommand

In an InstantCommand, the method isFinished() returns true by default so execute() will only run once. Since the initialize method always runs once, the executeable code can be put there too.

Uses

This command is useful for setting pneumatic, running motors for Button.whileHeld.

TimedCommand

TimedCommand runs a command for a specified time. The constructor for this class takes in the runtime in seconds of the command.

CommandGroup

Simply put, a Command Group is used to run multiple commands easily. This class allows to run commands one after another (sequentially) or simultaneously (in parallel). This class does not have any abstract methods but has the addSequential() and addParallel() methods. Consult ScreenSteps for more info.

These are very helpful for autonomous, where you can break all the subroutines into different commands that can be used in multiple autonomous command groups.

Command (Generic)

Generic Commands give the ability to have more freedom in implementation. This is the most “bare bones” command with all other command implementations extending this.

Subsystems

This class defines a major component of the robot. A good example of a subsystem is the driveline, or a claw if the robot has one.

Subsystems get activated by Commands. If you use the setDefaultCommand method inside a subsystem’s initDefaultCommand method, then that command will run if the subsystem isn’t used in any other command at the time (Note: this is only if isFinished() returns false). This is useful for subsystems such as drivetrains that require variable input.