如何从单独的java类调用方法_Java_Class_Methods

如何从单独的java类调用方法

java class methods

如何从单独的java类调用方法,java,class,methods,Java,Class,Methods,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Race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);

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

Race

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!");
        }
    }
}

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

函数调用尚未进行

您应该编写此代码来调用函数

event.Race();

希望它能解决问题。

RacingEvent

不会初始化其

字段。您可能希望将调用者可用的值（在那里也被称为

）传递给构造函数，并将

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;
 }

这样称呼它：

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

简化解决方案：

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();
  }
}

import java.awt.*；
导入java.util.Random；
类SimpleWindow{
公共SimpleWindow（inti，inti1，字符串赢家）{
//要更改已创建方法的主体，请使用文件|设置|文件模板。
}
公共静态无效延迟（int i）{
//要更改已创建方法的主体，请使用文件|设置|文件模板。
}
公共无效移动到（int i，int i1）{
//要更改已创建方法的主体，请使用文件|设置|文件模板。
}
public void writeText（字符串s）{
//要更改已创建方法的主体，请使用文件|设置|文件模板。
}
public void waitForMouseClick（）{
//要更改已创建方法的主体，请使用文件|设置|文件模板。
}
}
甲鱼类{
公共彩色甲鱼（简单黑白、整数i、整数Y、红色）{
//要更改已创建方法的主体，请使用文件|设置|文件模板。
}
公共彩色海龟（SimpleWindow、int i、int i1）{
super（w，i，i1）；
}
}
职业赛马场{
私家侦探；
公共赛马场（SimpleWindow、int yStart、int yFinish）{
//要更改已创建方法的主体，请使用文件|设置|文件模板。
}
public int getyFinish（）{
返回yFinish；
}
公共无效绘图（简单窗口）{
//要更改已创建方法的主体，请使用文件|设置|文件模板。
}
}
甲鱼{
私营企业；
公乌龟（SimpleWindow，int i，int i1）{
//要更改已创建方法的主体，请使用文件|设置|文件模板。
}
海龟（）{
}
公共空间{
//要更改已创建方法的主体，请使用文件|设置|文件模板。
}
公共int getY（）{
返回y；
}
公共空位前进（内线1）{
//要更改已创建方法的主体，请使用文件|设置|文件模板。
}
}
类RacingEvent{
私人住宅区；
私人马场;；
私人海龟t1=新海龟（w，200400）；
私人海龟t2=新海龟（w，300，400）；
公共赛马项目（赛马场、海龟t1、海龟t2）{
这是1.t1=t1；
这1.t2=t2；
this.track=轨道；
}
公开竞逐（）{
t1.penDown（）；
t2.penDown（）；
Random rand=新的Random（）；
海龟t1=新海龟（w，200400）；
海龟t2=新海龟（w，300，400）；
而（t1.getY（）>track.getyFinish（）&&t2.getY（）>track.getyFinish（））{
int turtle1=兰特nextInt（3）；
int turtle2=兰特nextInt（3）；
t1.前锋（套头衫1）；
t2.向前（套头衫2）；
简单延时（10）；
}
int diff1=t1.getY（）-track.getyFinish（）；
int diff2=t2.getY（）-track.getyFinish（）；
SimpleWindow=新的SimpleWindow（200100，“获胜者”）；
如果（t1.getY（））什么似乎不起作用？显示并使用您尝试过的内容？您不能调用event.Race（）；？尝试过，但我得到了一个java.lang。NullPointerException@Rob你从哪里得到NPE？NPE的调用堆栈是什么？+1哦，你是对的。它被用在'Turtle t1=new Turtle（w，200400）在初始化之前。对我的RacingEvent类做了一些小的修改，但后来我让它工作了。谢谢大家！酷的是，接受的答案并不能解决问题：D
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();
  }
}