nullpointerexception如何在java中运行具有多个公共类的程序?
我是java的新手。我编写了以下程序:
import java.util.ArrayList;
import java.io.*;
import java.util.*;
public class dotcombust{
GameHelper helper=new GameHelper();
ArrayList<Dotcom> dotcomlist;
int nofguess=0;
private void setup(){
Dotcom one =new Dotcom();
dotcomlist.add(one);
Dotcom two= new Dotcom();
dotcomlist.add(two);
Dotcom three= new Dotcom();
dotcomlist.add(three);
for(Dotcom obj : dotcomlist)
{
obj.setname();
ArrayList<String> loc= helper.placeDotCom(3);
obj.setlocation(loc);
}
}
private void startplaying(){
while(!dotcomlist.isEmpty())
{
nofguess++;
String guess=helper.getUserInput("Enter a guess ");
checkuser(guess);
}
finish();
}
private void checkuser(String guess){
String result="miss";
for(Dotcom obj : dotcomlist)
{
result=obj.checkyourself(guess);
if(result.equals("kill"))
{
System.out.println("You killed " + obj.name);
dotcomlist.remove(obj);
break;
}
else if(result.equals("hit"))
{
break;
}
}
if(result.equals("hit") || result.equals("miss"))
{
System.out.println(result);
}
}
private void finish(){
System.out.println("You took " + nofguess + "guesses. If they are below 10, congrats. Otherwise you suck balls. No offense.");
}
public static void main(String[] args){
dotcombust game;
game=new dotcombust();
game.setup();
game.startplaying();
}
}
当我运行这个程序时,我得到了java。位于DotCombum的lang.NullPointerException。setup()和dotcombum。startplaying()语句。 我认为类Dotcom和Gamehelper与错误无关,因此没有在这里显示它们。 请帮我解决这个问题。 另外,我想知道是否有可能在不同的源文件中编写类Dotcom和Gamehelper,但在代码中使用它?如果是,怎么办
# 1 楼答案
您需要实例化dotcomlist
# 2 楼答案
安装程序()中的dotcomlist为空
加:
在设置()的第一行