extending CANJaguar subclass

Technical Java
#1

I am trying to add methods to help with reading our robots actual speed off of a CANJaguar in fps. The issue I am having now is that it is not building becasue it needs a constructor, but if I am inheriting the class shouldn’t they already exist. What i want to be able to do is when i call a CANJaguar object, e.g. leftMotor.getFps(), it will return the fps data to me. This is my code so far.

Any help is greatly appreciated.


/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package edu.wpi.first.wpilibj;
import edu.wpi.first.wpilibj.can.CANTimeoutException;
import edu.wpi.first.wpilibj.can.JaguarCANProtocol;


/**
 *
 * @author rudun
 */
public class fps extends CANJaguar {

    final static double PI = Math.PI;
    private double WheelSize;
     /**
     * Get the speed of your robot.
     *
     * @return The speed of the robot in fps.
     */
    public double getFps() throws CANTimeoutException {
        byte] dataBuffer = new byte[8];
        byte dataSize;
        double rpms;

        dataSize = getTransaction(JaguarCANProtocol.LM_API_STATUS_SPD, dataBuffer);
        if (dataSize == 4) {
            rpms = unpackFXP16_16(dataBuffer);
        } else {
            rpms = 0.0;
        }
        
        double fps = 0;
        fps = (rpms *(WheelSize * PI))/(60 * 12);
        return fps;
    }
    
    public void setWheelSize(double WheelSizeInInches) {
        WheelSize = WheelSizeInInches;
        }
}

and this is my current compiler output


init:
clean:
init:
clean:
Created dir: C:\Users\kyle\Documents\NetBeansProjects\fpstest\build
Compiling 2 source files to C:\Users\kyle\Documents\NetBeansProjects\fpstest\build
C:\Users\kyle\Documents\NetBeansProjects\fpstest\src\edu\wpi\first\wpilibj\fps.java:13: error: no suitable constructor found for CANJaguar()
public class fps extends CANJaguar {
    constructor CANJaguar.CANJaguar(int,ControlMode) is not applicable
      (actual and formal argument lists differ in length)
    constructor CANJaguar.CANJaguar(int) is not applicable
      (actual and formal argument lists differ in length)
1 error
C:\Users\kyle\sunspotfrcsdk\ant\compile.xml:48: Compile failed; see the compiler error output for details.
BUILD FAILED (total time: 8 seconds)
#2

In this case you need to explicitly define at least one constructor for your subclass (fps).

Why? Because if you don’t specify a constructor in a subclass, Java makes a default one for you that doesn’t take any arguments. But that default no-argument constructor expects to call the no-argument constructor for all of the superclasses (CANJaguar in your case). CANJaguar doesn’t have a no-argument constructor, only the two constructors CANJaguar(int, ControlMode) and CANJaguar(int). That’s what the compiler error message is telling you - that CANJaguar has “no suitable constructor” for a default no-argument subclass constructor to call.

So you need to do something like this:


public class fps extends CANJaguar {
   
   public fps(int id) throws Exception {
         super(id);
   }

...
}

Hope that helps!

  • Ron
    Team #2607 controls mentor
#3

Thanks Ron. It now works, and even my math which is always a culprit in slowing me down was right. Here is what the whole thing is to anyone intrested in using the encoder on the Jaguar to calculate fps.


/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package edu.wpi.first.wpilibj;
import edu.wpi.first.wpilibj.can.CANTimeoutException;
import edu.wpi.first.wpilibj.can.JaguarCANProtocol;


/**
 *
 * @author rudun, 1203
 */
public class FPS extends CANJaguar{

    final static double PI = Math.PI;
    private double WheelSize;
    
    public FPS(int id) throws CANTimeoutException {
        super(id);
   }
     /**
     * Get the speed of your robot.
     *
     * @return The speed of the robot in fps.
     */
    public double getFps() throws CANTimeoutException {
        byte] dataBuffer = new byte[8];
        byte dataSize;
        double rpms;

        dataSize = getTransaction(JaguarCANProtocol.LM_API_STATUS_SPD, dataBuffer);
        if (dataSize == 4) {
            rpms = unpackFXP16_16(dataBuffer);
        } else {
            rpms = 0.0;
        }
        
        double fps = 0;
        fps = (rpms *(WheelSize * PI))/(60 * 12);
        return fps;
    }
    
    public void setWheelSize(double WheelSizeInInches) {
        WheelSize = WheelSizeInInches;
        }
}
#4