问题
I have some problems with calculating cosinus 90 in Java using Math.cos function :
public class calc{
private double x;
private double y;
public calc(double x,double y){
this.x=x;
this.y=y;
}
public void print(double theta){
x = x*Math.cos(theta);
y = y*Math.sin(theta);
System.out.println("cos 90 : "+x);
System.out.println("sin 90 : "+y);
}
public static void main(String[]args){
calc p = new calc(3,4);
p.print(Math.toRadians(90));
}
}
When I calculate cos90 or cos270, it gives me absurb values. It should be 0. I tested with 91 or 271, gives a near 0 which is correct.
what should I do to make the output of cos 90 = 0? so, it makes the output x = 0 and y = 4.
Thankful for advice
回答1:
What you're getting is most likely very, very small numbers, which are being displayed in exponential notation. The reason you're getting them is because pi/2 is not exactly representable in IEEE 754 notation, so there's no way to get the exact cosine of 90/270 degrees.
回答2:
Just run your source and it returns:
cos 90 : 1.8369701987210297E-16
sin 90 : 4.0
That's absolutely correct. The first value is nearly 0. The second is 4 as expected.
3 * cos(90°) = 3 * 0 = 0
Here you have to read the Math.toRadians() documentation which says:
Converts an angle measured in degrees to an approximately equivalent angle measured in radians. The conversion from degrees to radians is generally inexact.
Update: You can use for example the MathUtils.round() method from the Apache Commons repository and round the output to say 8 decimals, like this:
System.out.println("cos 90 : " + MathUtils.round(x, 8));
That will give you:
cos 90 : 0.0
sin 90 : 4.0
回答3:
Try this:
public class calc
{
private double x;
private double y;
public calc(double x,double y)
{
this.x=x;
this.y=y;
}
public void print(double theta)
{
if( ((Math.toDegrees(theta) / 90) % 2) == 1)
{
x = x*0;
y = y*Math.sin(theta);
}
else if( ((Math.toDegrees(theta) / 90) % 2) == 0)
{
x = x*Math.cos(theta);
y = y*0;
}
else
{
x = x*Math.cos(theta);
y = y*Math.sin(theta);
}
System.out.println("cos 90 : "+x);
System.out.println("sin 90 : "+y);
}
public static void main(String[]args)
{
calc p = new calc(3,4);
p.print(Math.toRadians(90));
}
}
来源：https://stackoverflow.com/questions/5263653/how-to-solve-cos-90-problem-in-java