我正在研究編程原理II的實驗,並且我有一個課程提供了一個點,包括設置點的方法和計算其他點之間的距離。計算距離在用類運行器測試時運行良好,但是當我使用其他類作爲對象時,我得到了距離公式的錯誤。Java數學錯誤
import java.lang.Math;
public class MyPoint {
private double x;
private double y;
public MyPoint(double dubx, double duby)
{
x=dubx;
y=duby;
}
public void setX(double dub) {
x = dub;
}
public void setY(double dub) {
y = dub;
}
public double getX() {
return x;
}
public double getY()
{
return y;
}
public double distance (MyPoint otherPoint)
{
return Math.sqrt(Math.pow((otherPoint.getX()-getX()),2)+(Math.pow((otherPoint.getY()-getY()),2)));
}
public MyPoint midpoint(MyPoint otherPoint)
{
MyPoint point = new MyPoint((otherPoint.getX()+getX()/2),(otherPoint.getY()+getY())/2);
return point;
}
}
這是我遇到錯誤的類。距離部分得到空指針異常。
下面是我通過什麼:
import java.lang.Math;
public class MyTriangle
{
private MyPoint v1;
private MyPoint v2;
private MyPoint v3;
public MyPoint getPoint1()
{
return v1;
}
public MyPoint getPoint2()
{
return v2;
}
public MyPoint getPoint3()
{
return v3;
}
public void setPoint1(double x, double y)
{
v1= new MyPoint(x,y);
}
public void setPoint2(double x, double y)
{
v2 = new MyPoint(x,y);
}
public void setPoint3(double x, double y)
{
v2= new MyPoint(x,y);
}
public double getArea()
{
double a= v2.distance(v3);
double b= v1.distance(v3);
double c= v1.distance(v2);
double s= (a+b+c)/2;
return Math.sqrt(s*(s-a)*(s-b)*(s-c));
}
}
public class TestMyTriangle
{
public static void main(String [] args)
{
MyTriangle tr1 = new MyTriangle();
tr1.setPoint1(17,17);
tr1.setPoint2(5,30);
tr1.setPoint3(5,17);
System.out.println("Area:\t"+tr1.getArea());
}
}
和錯誤:
Exception in thread "main" java.lang.NullPointerException
at MyPoint.distance(MyPoint.java:34)
at MyTriangle.getArea(MyTriangle.java:37)
at TestMyTriangle.main(TestMyTriangle.java:9)
我似乎無法推測出來。請幫忙。
'公共無效setPoint3(雙X,雙Y) { V2 =新MyPoint(X,Y); } ' –
使用調試器查看哪個對象沒有被初始化。 –