Java：调用方法并从另一个类实例化对象时出现问题

Question

I am an AP Computer Programming student and I am having quite a bit of trouble understanding how to call methods to a driver program defined in one class , as well as create objects in the driver class from the constructor of the non-driver class. My book has the following class, with the program's intent being to simulate the flipping of a coin:

import java.util.Random;

public class Coin{

        private int HEADS = 0;
        private int TAILS = 1;

        private int face;

        Coin mycoin = new Coin();

        public Coin(){

        flip();
        }

        public void flip(){

            face = (int) (Math.random() * 2);
        }

        public boolean isHeads(){

            return (face == HEADS);
        }

        public String toString(){

            String faceName;

            if (face == HEADS)
                faceName = "Heads";
            else
                faceName = "Tails";

            return faceName;
        }
}

Here is an example driver program from the book as well:

public class FlipRace
{
  public static void main(String[] args)
  {
    final int NUM_FLIPS = 1000;
    int heads = 0, tails = 0;

    Coin myCoin = new Coin();

    for (int count = 1; count <= NUM_FLIPS; count++)
    {
      myCoin.flip();

      if (myCoin.isHeads())
        heads++;
      else
        tails++;
    }

    System.out.println("The number of flips: " + NUM_FLIPS);
    System.out.println("The number of heads: " + heads);
    System.out.println("The number of tails: " + tails);   
  }
}

The problem I have is that when I try to recreate the driver program or make any driver program, the driver program seems to be unable to call upon the customized classes of the constructor. I get errors like:

cannot find symbol
  symbol:  Class Coin
  location:  Class (name of driver program)

I honestly have no idea what the problem is. It had been said to me that a separate .java file was needed in order to access the constructor, but I couldn't find a way to do that. Was that person wrong? Am I supposed to put the main method and the constructor all on one program? If not that, how do I call upon methods from another class?

I've been struggling with this for almost a week, so any help would be appreciated.

EDIT : The spelling errors in the for loop were my own. They are not present in the actual program. I have now fixed them.

Answer 1

1. Make sure the driver and the Coin class are in the same package (or that you import the package Coin is in), it appears that you have them both in the default package.
2. Compile Coin.java before (or at the same time) as the driver javac *.java

3. Make sure you specify a classpath that includes the current folder when you execute the driver like

   java -cp . FlipRace

Finally,

for (inc count = 1; counr <= NUM_FLIPS; count++)

should be

for (int count = 1; count <= NUM_FLIPS; count++)

I haven't exhaustively searched your code for more typos.

Answer 2

Try out this by reoving this code from Coin Class

Coin mycoin = new Coin();

    public Coin(){

    flip();
    }

and made changes in the line of for loop in FlipRace

    for (int count = 1; count <= NUM_FLIPS; count++)

Answer 3

I think the best advice that can be given here is to research the basics of Java packages. This is a good place to start: Java packages tutorial

It covers such topics as:

• Creating and Using Packages
• Using Package Members
• Managing Source and Class Files

Having read that, you should be able to understand the problems you are facing.