How to call a method from a separate class java

Question

I'm trying to call a method from a separate class in java but it doesn't seem to work, or I'm doing something wrong. What I want to achieve is to call my Race method which is in the RacingEvent class to my main program (Check the comment in the main program).

Here is the class:

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!"); } } }

And here is the main program where I need to call the method:

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*/ } }

What didn't seem to work? Show use what you tried?

Rohit Jain
– Rohit Jain

2012-11-20 18:00:50 +00:00
Commented Nov 20, 2012 at 18:00 — Rohit Jain
– Rohit Jain, Commented Nov 20, 2012 at 18:00
You can't call event.Race(); ?

mprivat
– mprivat

2012-11-20 18:01:38 +00:00
Commented Nov 20, 2012 at 18:01 — mprivat
– mprivat, Commented Nov 20, 2012 at 18:01
Tried it but then I get an java.lang.NullPointerException

Rob
– Rob

2012-11-20 18:03:14 +00:00
Commented Nov 20, 2012 at 18:03 — Rob
– Rob, Commented Nov 20, 2012 at 18:03
@Rob where do you get NPE ??

PermGenError
– PermGenError

2012-11-20 18:05:17 +00:00
Commented Nov 20, 2012 at 18:05 — PermGenError
– PermGenError, Commented Nov 20, 2012 at 18:05
What is the call stack of the NPE?

TheBlastOne
– TheBlastOne

2012-11-20 18:05:34 +00:00
Commented Nov 20, 2012 at 18:05 — TheBlastOne
– TheBlastOne, Commented Nov 20, 2012 at 18:05

droidchef · Accepted Answer · 2012-11-20 18:06:33Z

2

When you do this

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

You are just creating and instantiating an object of the RacingEvent class.

The function call is yet to be made.

You should write this to call the function.

event.Race();

Hope it solves the problem.

answered Nov 20, 2012 at 18:06

droidchef

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2 Comments

Rob Over a year ago

Did some minor modifications to my RacingEvent class but then I got it working. Thanks everyone!

TheBlastOne Over a year ago

Cool thing is that the accepted answer does not solve the problem :D

TheBlastOne · Accepted Answer · 2012-11-20 18:09:24Z

RacingEvent does not initialize its w field. You might want to pass the value that is available to the caller (called w there, too) to the constructor and set w to the argument passed in.

In detail:

Change the constructor to

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

and call it like this:

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

+1 Oh you are correct. It's being used at ` Turtle t1 = new Turtle(w, 200, 400);` before initialization.

Roman C · Accepted Answer · 2012-11-20 18:20:46Z

Simplified solution:

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(); } }

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