import java.util.*;public class Test
{
int PointNum;
float PointX;
float PointY;
float setPointX()
{
Random r=new Random();
return r.nextFloat()*12;
}
float setPointY()
{
Random r=new Random();
return r.nextFloat()*10;
}
public static void main(String args[])
{
int Userinput,inNum,Size=50;
Test[] Dot =new Test[Size];
System.out.println("There will be " + Size + " random points");
for(int m=0;m<Dot.length;++m)
{
Dot[m].PointNum=m+1;
Dot[m].PointX=Dot[m].setPointX();
Dot[m].PointY=Dot[m].setPointY();
}
for(int m=0;m<Dot.length;++m)
{
System.out.println(Dot[m].PointNum+":" +Dot[m].PointX +"," + Dot[m].PointY);
}
}
}
使用的是JCreator3。50pro,编译通过,运行结果:
There will be 50 random points
Exception in thread "main"java.lang.NullPointerException
at Test.main(Test.java:32)
{
int PointNum;
float PointX;
float PointY;
float setPointX()
{
Random r=new Random();
return r.nextFloat()*12;
}
float setPointY()
{
Random r=new Random();
return r.nextFloat()*10;
}
public static void main(String args[])
{
int Userinput,inNum,Size=50;
Test[] Dot =new Test[Size];
System.out.println("There will be " + Size + " random points");
for(int m=0;m<Dot.length;++m)
{
Dot[m].PointNum=m+1;
Dot[m].PointX=Dot[m].setPointX();
Dot[m].PointY=Dot[m].setPointY();
}
for(int m=0;m<Dot.length;++m)
{
System.out.println(Dot[m].PointNum+":" +Dot[m].PointX +"," + Dot[m].PointY);
}
}
}
使用的是JCreator3。50pro,编译通过,运行结果:
There will be 50 random points
Exception in thread "main"java.lang.NullPointerException
at Test.main(Test.java:32)
{
int PointNum;
float PointX;
float PointY;
float setPointX()
{
Random r=new Random();
return r.nextFloat()*12;
}
float setPointY()
{
Random r=new Random();
return r.nextFloat()*10;
}
public static void main(String args[])
{
int Userinput,inNum,Size=50;
Test[] Dot =new Test[Size]; for (int i=0; i<Dot.lenght; i++) {
Dot[i] = new Test();
} System.out.println("There will be " + Size + " random points");
for(int m=0;m<Dot.length;++m)
{
Dot[m].PointNum=m+1;
Dot[m].PointX=Dot[m].setPointX();
Dot[m].PointY=Dot[m].setPointY();
}
for(int m=0;m<Dot.length;++m)
{
System.out.println(Dot[m].PointNum+":" +Dot[m].PointX +"," + Dot[m].PointY);
}
}
}
我只是声明了一个Test对象数组,却没有构造这些Test对象。