Java help

Technical Java
#1

I am part of team 4592 and I took on the task of being programming captain. I don’t know much and i need some help. I need to run a motor while a button is being pressed and held. I’ve gone through wpilib and can’t figure it out. Thanks to anyone who can help it is greatly appreciated.

#2

WPILib resources:
Screensteps
API Reference (Java)
API Reference (C++)

Using the command based architecture, you need to first create a subsystem that the motor belongs to


public class MyMotorSubsystem extends Subsystem {
  CANSomething myMotor;
  public MyMotorSubsystem {
    myMotor = new CANSomething(RobotMap.CAN_ID_MY_MOTOR);
  }
  public void setMotor(double value) {
    myMotor.set(value);
  }
}

Then you need a command to run the motor.


public class CommandBase extends Command {
  public static MyMotorSubsystem myMotorSubsystem;
  public static void init() {
    myMotorSubsystem = new MyMotorSubsystem();
  }
}

public class RunMotorCommand extends CommandBase {
  JoystickButton runMotorButton;
  public RunMotorCommand(JoystickButton runMotorButton) {
    this.runMotorButton = runMotorButton;
    runMotorButton.whenPressed(this);
  }
  void initialize() {
    requires(myMotorSubsystem);
  }
  void run() {
    myMotorSubsystem->setMotor(1.0);
  }
  void isFinished() {
    return runMotorButton.get();
  }
  void end() {
    myMotorSubsystem->setMotor(0.0);
  }
  void interrupted() {
    myMotorSubsystem->setMotor(0.0);
  }
}

Then you need to create an instance of the command


// somewhere in OI.java
new RunMotorCommand(new JoystickButton(myJoystick, something));
#3

Here is what the above would look like in Java:


public class MyMotorSubsystem extends Subsystem {
  ControllerType myMotor;
  public MyMotorSubsystem () {
    myMotor = new ControllerType(RobotMap.ID_MY_MOTOR);
  }
  public void setMotor(double value) {
    myMotor.set(value);
  }
}

Command to run the motor.


public class CommandBase extends Command {
  public static MyMotorSubsystem myMotorSubsystem;
  public static void init() {
    myMotorSubsystem = new MyMotorSubsystem();
  }
}

public class RunMotorCommand extends CommandBase {
  JoystickButton runMotorButton;
  public RunMotorCommand(JoystickButton runMotorButton) {
    this.runMotorButton = runMotorButton;
    runMotorButton.whenPressed(this);
  }
  void initialize() {
    requires(myMotorSubsystem);
  }
  void execute() {
    myMotorSubsystem.setMotor(1.0);
  }
  boolean isFinished() {
    return !runMotorButton.get();
  }
  void end() {
    myMotorSubsystem.setMotor(0.0);
  }
  void interrupted() {
    myMotorSubsystem.setMotor(0.0);
  }
}

Create an instance of the command


// somewhere in OI.java
new RunMotorCommand(new JoystickButton(myJoystick, something));

My team does not use the CommandBase, and we usually instantiate subsystems in the Robot.java file, so I am not 100% sure this is right, but the basic idea should be apparent. Basically, create a command that in the execute will call a method from a subsystem that sets the motor to the value you want, which is triggered by a button and will end when that button isn’t pressed.

#4

2016 was our first year with Java too, and being the sole programmer, I kinda got thrown into the fire. Here’s our code from 2016. Its mostly very simple command-based stuff, but if you have any questions you can PM me. Hope that helps!

#5