如何从单独的java类调用方法

Question

我试图在java中从一个单独的类调用一个方法，但它似乎不起作用，或者我做错了什么。我想要实现的是将Race类中的RacingEvent方法调用到我的主程序（检查主程序中的注释）

下面是课堂：

import java.util.Random;

public class RacingEvent {
    private SimpleWindow w;
    private RaceTrack track;
    private Turtle t1 = new Turtle(w, 200, 400);
    private Turtle t2 = new Turtle(w, 300, 400);

    public RacingEvent(RaceTrack track, Turtle t1, Turtle t2) {
        this.t1 = t1;
        this.t2 = t2;
        this.track = track;
 }

    public void Race() {
        t1.penDown();
        t2.penDown();
        Random rand = new Random();

        Turtle t1 = new Turtle(w, 200, 400);
        Turtle t2 = new Turtle(w, 300, 400);

        while (t1.getY() > track.getyFinish() && t2.getY() > track.getyFinish()) {
            int turtle1 = rand.nextInt(3);
            int turtle2 = rand.nextInt(3);
            t1.forward(turtle1);
            t2.forward(turtle2);

            SimpleWindow.delay(10);
        }


        int diff1 = t1.getY() - track.getyFinish();
        int diff2 = t2.getY() - track.getyFinish();

        SimpleWindow w = new SimpleWindow(200, 100, "Winner");

        if (t1.getY() <= track.getyFinish()) {
            w.moveTo(20, 40);
            w.writeText("T1 won with a " + diff2 + " step(s) lead!");
        } else if (t2.getY() <= track.getyFinish()) {
            w.moveTo(20, 40);
            w.writeText("T2 won with a " + diff1 + " step(s) lead!");
        }
    }
}

这是我需要调用方法的主程序：

public class TurtleRace {
    public static void main(String[] args) {
        SimpleWindow w = new SimpleWindow(600, 600, "TurtleRace");
        int yStart = 400; 
        int yFinish = 100; 

        RaceTrack track = new RaceTrack(w, yStart, yFinish);
        ColorTurtle t1 = new ColorTurtle(w, 250, yStart, java.awt.Color.RED);
        ColorTurtle t2 = new ColorTurtle(w, 350, yStart, java.awt.Color.BLUE);

        track.draw(w);
        w.waitForMouseClick();

        RacingEvent event = new RacingEvent(track, t1, t2);
        /*Call Race Method*/
    }
}

Answer 1

RacingEvent不初始化其w字段。您可能希望将调用者可用的值（在那里也被称为w）传递给构造函数，并将w设置为传入的参数

详细内容：

将构造函数更改为

public RacingEvent(SimpleWindow w, RaceTrack track, Turtle t1, Turtle t2) {
        this.w = w;
        this.t1 = t1;
        this.t2 = t2;
        this.track = track;
 }

这样称呼：

 RacingEvent event = new RacingEvent(w, track, t1, t2);
 event.race();

Answer 2

当你这么做的时候

RacingEvent event = new RacingEvent(track, t1, t2);

您只是在创建和实例化RacingEvent类的一个对象

函数调用尚未完成

你应该写这个来调用函数

event.Race();

希望它能解决问题

Answer 3

简化的解决方案：

import java.awt.*;
import java.util.Random;

class SimpleWindow {
  public SimpleWindow(int i, int i1, String winner) {
    //To change body of created methods use File | Settings | File Templates.
  }

  public static void delay(int i) {
    //To change body of created methods use File | Settings | File Templates.
  }

  public void moveTo(int i, int i1) {
    //To change body of created methods use File | Settings | File Templates.
  }

  public void writeText(String s) {
    //To change body of created methods use File | Settings | File Templates.
  }

  public void waitForMouseClick() {
    //To change body of created methods use File | Settings | File Templates.
  }
}
class ColorTurtle extends Turtle {
  public ColorTurtle(SimpleWindow w, int i, int yStart, Color red) {
    //To change body of created methods use File | Settings | File Templates.
  }

  public ColorTurtle(SimpleWindow w, int i, int i1) {
    super(w, i, i1);
  }
}

class RaceTrack {
  private int yFinish;

  public RaceTrack(SimpleWindow w, int yStart, int yFinish) {
    //To change body of created methods use File | Settings | File Templates.
  }

  public int getyFinish() {
    return yFinish;
  }

  public void draw(SimpleWindow w) {
    //To change body of created methods use File | Settings | File Templates.
  }
}
class Turtle {
  private int y;

  public Turtle(SimpleWindow w, int i, int i1) {
    //To change body of created methods use File | Settings | File Templates.
  }

  Turtle() {
  }

  public void penDown() {
    //To change body of created methods use File | Settings | File Templates.
  }

  public int getY() {
    return y;
  }

  public void forward(int turtle1) {
    //To change body of created methods use File | Settings | File Templates.
  }
}
class RacingEvent {
  private SimpleWindow w;
  private RaceTrack track;
  private Turtle t1 = new Turtle(w, 200, 400);
  private Turtle t2 = new Turtle(w, 300, 400);

  public RacingEvent(RaceTrack track, Turtle t1, Turtle t2) {
    this.t1 = t1;
    this.t2 = t2;
    this.track = track;
  }

  public void Race() {
    t1.penDown();
    t2.penDown();
    Random rand = new Random();

    Turtle t1 = new Turtle(w, 200, 400);
    Turtle t2 = new Turtle(w, 300, 400);

    while (t1.getY() > track.getyFinish() && t2.getY() > track.getyFinish()) {
      int turtle1 = rand.nextInt(3);
      int turtle2 = rand.nextInt(3);
      t1.forward(turtle1);
      t2.forward(turtle2);

      SimpleWindow.delay(10);
    }


    int diff1 = t1.getY() - track.getyFinish();
    int diff2 = t2.getY() - track.getyFinish();

    SimpleWindow w = new SimpleWindow(200, 100, "Winner");

    if (t1.getY() <= track.getyFinish()) {
      w.moveTo(20, 40);
      w.writeText("T1 won with a " + diff2 + " step(s) lead!");
    } else if (t2.getY() <= track.getyFinish()) {
      w.moveTo(20, 40);
      w.writeText("T2 won with a " + diff1 + " step(s) lead!");
    }
  }
}
public class TurtleRace {
  public static void main(String[] args) {
    SimpleWindow w = new SimpleWindow(600, 600, "TurtleRace");
    int yStart = 400;
    int yFinish = 100;

    RaceTrack track = new RaceTrack(w, yStart, yFinish);
    ColorTurtle t1 = new ColorTurtle(w, 250, yStart, java.awt.Color.RED);
    ColorTurtle t2 = new ColorTurtle(w, 350, yStart, java.awt.Color.BLUE);

    track.draw(w);
    w.waitForMouseClick();

    RacingEvent event = new RacingEvent(track, t1, t2);
    /*Call Race Method*/
    event.Race();
  }
}