我试图创建一个2D矢量数学库，并制作了适当的类和函数来执行特定的计算，但是当我尝试从我的主类调用这些所述方法时，没有任何东西被返回或者如果它确实得到了回来了，它会是0.我不知道我哪里出错了，有人可以帮忙吗？
public class Vector2D {
public double x = 0.0;
public double y = 0.0;
public Vector2D(){
}
public Vector2D(double vectorX, double vectorY){
vectorX = x;
vectorY = y;
}
}
这是我的实际矢量本身的课程。
public class Vector2DMaths {
public static Vector2D addition2D(Vector2D vec1, Vector2D vec2){
Vector2D vecAddResult2D = new Vector2D();
vecAddResult2D.x = vec1.x + vec2.x;
vecAddResult2D.y = vec1.y + vec2.y;
return vecAddResult2D;
}
public static Vector2D subtraction2D(Vector2D vec3, Vector2D vec4){
Vector2D vecSubtractResult2D = new Vector2D();
vecSubtractResult2D.x = vec3.x - vec4.x;
vecSubtractResult2D.y = vec3.y - vec4.y;
return vecSubtractResult2D;
}
public static double findMagnitude2D(Vector2D vec5){
double d;
double magnitude;
d = (Math.pow((vec5.x), 2) + Math.pow((vec5.y), 2));
magnitude = Math.sqrt(d);
return magnitude;
}
public static double dotProduct2D(Vector2D a, Vector2D b){
double aDOTb;
double aMag;
double bMag;
double angle;
aDOTb = (a.x * b.x) + (a.y + b.y);
aMag = findMagnitude2D(a);
bMag = findMagnitude2D(b);
angle = Math.acos((aDOTb)/(aMag * bMag));
angle = angle * (180/Math.PI);
return angle;
}
public static Vector2D unitNormal2D(Vector2D vec6){
double vec6Mag;
Vector2D unitN2D = new Vector2D();
vec6Mag = findMagnitude2D(vec6);
unitN2D.x = vec6.x / vec6Mag;
unitN2D.y = vec6.y / vec6Mag;
return unitN2D;
}
public static Vector2D rotation(Vector2D vec7, double angle){
Vector2D rotatedVec = new Vector2D();
rotatedVec.x = (Math.cos(angle)*vec7.x) - (Math.sin(angle)*vec7.y);
rotatedVec.y = (Math.sin(angle)*vec7.x) - (Math.cos(angle)*vec7.y);
return rotatedVec;
}
public static Vector2D velocityVector(double speed, double launchAngle){
Vector2D vec8 = new Vector2D();
Vector2D velocityVec = new Vector2D();
double vMag, velocity;
vec8.x = Math.cos(launchAngle);
vec8.y = Math.sin(launchAngle);
vMag = findMagnitude2D(vec8);
velocity = speed / vMag;
velocityVec.x = vec8.x * velocity;
velocityVec.y = vec8.y * velocity;
return velocityVec;
}
}
这是我的实际数学库的课程。
switch (options){
case "1":
System.out.println("Vector 1: (3.3,6.2)");
System.out.println("Vector 2: (4.2,12.7)");
Vector2D option1Vec1 = new Vector2D(3.3,6.2);
Vector2D option1Vec2 = new Vector2D(4.2, 12.7);
System.out.println("The product of these two vectors are " + Vector2DMaths.addition2D(option1Vec1, option1Vec2));
break;
case "2":
System.out.println("Vector 1: (1.0, 4.5, 8.3)");
System.out.println("Vector 2: (12.6, -4.5, 6.7)");
Vector3D option2Vec1 = new Vector3D(1.0, 4.5, 8.3);
Vector3D option2Vec2 = new Vector3D(12.6, -4.5, 6.7);
System.out.println("The product of these two vectors are " + Vector3DMaths.addition3D(option2Vec1, option2Vec2));
break;
case "3":
System.out.println("Vector 1: (3.3,6.2)");
System.out.println("Vector 2: (4.2,12.7)");
Vector2D option3Vec1 = new Vector2D(3.3,6.2);
Vector2D option3Vec2 = new Vector2D(4.2, 12.7);
System.out.println("The difference of these two vectors are " + Vector2DMaths.subtraction2D(option3Vec1, option3Vec2));
break;
case "4":
System.out.println("Vector 1: (1.0, 4.5, 8.3)");
System.out.println("Vector 2: (12.6, -4.5, 6.7)");
Vector3D option4Vec1 = new Vector3D(1.0, 4.5, 8.3);
Vector3D option4Vec2 = new Vector3D(12.6, -4.5, 6.7);
System.out.println("The difference of these two vectors are " + Vector3DMaths.subtraction3D(option4Vec1, option4Vec2));
break;
case "5":
System.out.println("Vector 1: (7.5,7.5)");
System.out.println("Vector 2: (12.0,0.0)");
Vector2D option5Vec1 = new Vector2D(7.5,7.5);
Vector2D option5Vec2 = new Vector2D(12.0,0.0);
System.out.println("The angle found by doing the dot product of these two vectors is " + Vector2DMaths.dotProduct2D(option5Vec1, option5Vec2));
break;
case "6":
System.out.println("Vector 1: (1.0, 4.5, 8.3)");
System.out.println("Vector 2: (12.6, -4.5, 6.7)");
Vector3D option6Vec1 = new Vector3D(1.0, 4.5, 8.3);
Vector3D option6Vec2 = new Vector3D(12.6, 0.0, 6.7);
System.out.println("The angle found by doing the dot product of these two vectors is " + Vector3DMaths.dotProduct3D(option6Vec1, option6Vec2));
break;
case "7":
System.out.println("Vector 1: (7.5,7.5)");
Vector2D option7Vec1 = new Vector2D(7.5,7.5);
System.out.println("The magnitude of this vector is " + Vector2DMaths.findMagnitude2D(option7Vec1));
break;
case "8":
System.out.println("Vector 1: (1.0, 4.5, 8.3)");
Vector3D option8Vec1 = new Vector3D(1.0, 4.5, 8.3);
System.out.println("The magnitude of this vector is " + Vector3DMaths.findMagnitude3D(option8Vec1));
break;
case "9":
System.out.println("Vector 1: (7.5,7.5)");
System.out.println("Vector 2: (12.0,0.0)");
Vector2D option9Vec1 = new Vector2D(7.5,7.5);
Vector2D option9Vec2 = new Vector2D(12.0,0.0);
System.out.println("The unit normals for these vectors are " + Vector2DMaths.unitNormal2D(option9Vec1) + " and " + Vector2DMaths.unitNormal2D(option9Vec2) + " respectively");
break;
case "10":
System.out.println("Vector 1: (1.0, 4.5, 8.3)");
System.out.println("Vector 2: (12.6, -4.5, 6.7)");
Vector3D option10Vec1 = new Vector3D(1.0, 4.5, 8.3);
Vector3D option10Vec2 = new Vector3D(12.6, 0.0, 6.7);
System.out.println("The unit normals for these vectors are " + Vector3DMaths.unitNormal3D(option10Vec1) + " and " + Vector3DMaths.unitNormal3D(option10Vec2) + " respectively");
break;
case "11":
System.out.println("Vector: (3.0,4.0)");
System.out.println("Angle: 60 degrees");
Vector2D option11Vec = new Vector2D(3.0,4.0);
double angle = 60.0;
System.out.println("After the rotation, the vector now has a quantity of " + Vector2DMaths.rotation(option11Vec, angle));
break;
case "12":
System.out.println("Speed: 20 m/s");
System.out.println("Angle: 45 degrees");
double speed = 20.0;
double launchAngle = 45.0;
System.out.println("The velocity vector from this speed and angle is " + Vector2DMaths.velocityVector(speed, launchAngle));
break;
}
我在这里制作了一个开关板，你可以调用不同的方法。当我返回一个Vector2D对象时，会返回一些不相干的东西，当我返回一个double时，将返回0.0。据我所知，数学是正确的，但我不知道如何获得实际值。
答案 0 :(得分：2)
首先，Vector2D类的构造函数是错误的。变量x和y永远不会更新。这就是为什么你得到所有双返回0的原因（注意：java将双精度初始化为零）。你的构造函数应该是：
public Vector2D(double vectorX, double vectorY) {
this.x = vectorX;
this.y = vectorY;
}
接下来，正如@Johnny Mopp建议您需要在toString()类中添加Vector2D方法，以便java正确打印矢量实例。否则，java只会打印对象的内存位置（看起来像是乱码）。这可以通过以下方式实现：
@override
public String toString() {
// Can add more fancy print formats here.
return this.x+" "+this.y;
}