在另一个类中使用主类的对象

Question

So we are trying to create an AI robot and I found out that Java isn't that easy as I tought. What I am trying to do is to get an object from another class.

Main class:

    package main;


   import lejos.hardware.Brick;
   import lejos.hardware.BrickFinder;
   import lejos.hardware.motor.EV3LargeRegulatedMotor;
   import lejos.robotics.RegulatedMotor;
   import movement.Forward;

   public final class Runner {


    public static void main(String[] args) {
        //create brick
        Brick brick = BrickFinder.getDefault();

        // create motors
        RegulatedMotor left = new EV3LargeRegulatedMotor(brick.getPort("A"));
        RegulatedMotor right = new EV3LargeRegulatedMotor(brick.getPort("D"));

        //initialize motors
        left.setAcceleration(400);
        right.setAcceleration(400);

        left.setSpeed(400);
        right.setSpeed(400);



    Forward forward = new Forward();
        forward.moveForward();

    }



}

but the other class is this

    package movement;


   import lejos.utility.Delay;
   import main.Runner;

   public class Forward{

    public int speed;



    public void moveForward(){
        //moves forward for 5 seconds, then floats until motor stops and then closes the motors
            left.backward();
            right.backward();

            Delay.msDelay(5000);

            left.flt();
            right.flt();

            left.close();
            right.close();



    }

}

I would like to use the object left and right to make a method which would move forward.

Answer 1

You could pass left and right into Forward:

Forward forward = new Forward(left, right);

and change Forward constructor:

public class Forward{

    public int speed;
    RegulatedMotor left;
    RegulatedMotor right;

    public Forward(RegulatedMotor l, RegulatedMotor r) {
        left = l;
        right = r;
    }

Answer 2

Your Forward class obviously needs a reference to the two motor instances. You should forward (no pun intended) them at construction time:

public class Forward {
    private final RegulatedMotor left;
    private final RegulatedMotor right;

    public Forward(RegulatedMotor left, RegulatedMotor right) {
        this.left = left;
        this.right = right;
    }

    public void moveForward() { ... }
}

Your foward metho now has access to them. Constructing such a Forward now must be done as following:

Forward forward = new Forward(left, right);

Answer 3

Firstly, you'd have to initialise them outside the "main" subroutine. And then you'd have to make them public and static.

public static RegulatedMotor left;
public static RegulatedMotor right;
public static void main(String[] args)
{
    left = new EV3LargeRegulatedMotor(brick.getPort("A"));
    right = new EV3LargeRegulatedMotor(brick.getPort("D"));
    //rest of code as normal.
}

And then to access them from another class I believe you'd use:

Runner.left.Whateverfunction();

For the "left" object and;

Runner.right.Whateverfunction();

For the "right" object.

It's possible that I got a couple of syntax errors because I'm mainly a C# programmer, but I believe this should more or less be accurate.