System.out.println（）不打印任何内容。

Question

This code compiles, but doesn't print anything into the terminal.

So my code is meant to compare the y co-ordinate of the robot with the y co-ordinate of the target.

public class Ex12 
{

  private byte isTargetNorth(IRobot robot)
  {

    if (robot.getLocationY() > robot.getTargetLocation().y) 
      {System.out.println("north");
      return 1;}

    else if (robot.getLocationY() == robot.getTargetLocation().y)
      {System.out.println("no");
      return 0;}

    else 
      {System.out.println("south");
      return -1;}

  }
}

Answer 1

I guess it is supposed to be:

public static void main(String[]args)
{

     IRobot robot = new IRobot().

     Ex12 instance = new Ex12().

     instance.isTargetNorth(robot);


}

   public class Ex12 
{

  public byte isTargetNorth(IRobot robot)
  {

    if (robot.getLocationY() > robot.getTargetLocation().y) 
      {System.out.println("north");
      return 1;}

    else if (robot.getLocationY() == robot.getTargetLocation().y)
      {System.out.println("no");
      return 0;}

    else 
      {System.out.println("south");
      return -1;}

  }
}

Answer 2

My guess is that you just wrote this function and you aren't calling it anywhere.

Make a main with:

public static void main(String[] args) {
    //Create robot instance, assuming a Robot implementation is
    //named Robot and has a default constructor.
    IRobot robot = new Robot();

    //Create instance of example class since your function is not static.
    Ex12 instance = new Ex12();
    instance.isTargetNorth(robot);
}

Answer 3

You have a method named isTargetNorth , but there is nothing that invokes it. You need to invoke the method. Create a main() method that invokes isTargetNorth . Compile the class, then you can run it from the command line. It's easier if you're using an IDE, though, since it will probably let you run the class from the IDE once you've created the main method. Assuming you have a Robot implementation:

public static void main(String[] args) {
    IRobot robot = new RobotImpl();
    isTargetNorth(robot);
}