深入学习java源码之Math.sin()与 Math.sqrt()

native关键字

凡是一种语言，都希望是纯。比如解决某一个方案都喜欢就单单这个语言来写即可。Java平台有个用户和本地C代码进行互操作的API，称为JNI

native关键字告诉编译器(其实是JVM)调用的是该方法在外部定义，这里指的是C。

Modifier and TypeMethod and Descriptionstatic doubleacos(double a) 返回值的反余弦值; 返回的角度在0.0到pi的范围内。 static intaddExact(int x, int y) 返回其参数的总和，如果结果溢出int，则抛出 int 。 static longaddExact(long x, long y) 返回其参数的总和，如果结果溢出long，则抛出 long 。 static doubleasin(double a) 返回值的正弦值; 返回角度在pi / 2到pi / 2的范围内。 static doubleatan(double a) 返回值的反正切值; 返回角度在pi / 2到pi / 2的范围内。 static doubleatan2(double y, double x) 返回从直角坐标(转换角度 theta x ， y )为极坐标 (R，θ-)。 static doublecbrt(double a) 返回 double值的多维数据集根。 static doubleceil(double a) 返回大于或等于参数的最小(最接近负无穷大) double值，等于一个数学整数。 static doublecopySign(double magnitude, double sign) 使用第二个浮点参数的符号返回第一个浮点参数。 static floatcopySign(float magnitude, float sign) 使用第二个浮点参数的符号返回第一个浮点参数。 static doublecos(double a) 返回角度的三角余弦。 static doublecosh(double x) 返回的双曲余弦 double值。 static doubleexp(double a) 返回欧拉的数字 e提高到一个 double价值。 static doubleexpm1(double x) 返回 e x -1。 static doublehypot(double x, double y) 返回sqrt( x 2 + y 2 )，没有中间溢出或下溢。 static doublelog(double a) 返回的自然对数(以 e为底) double值。 static doublelog10(double a) 返回一个 double的基数10对数值。 static doublelog1p(double x) 返回参数和1的和的自然对数。 static doublepow(double a, double b) 将第一个参数的值返回到第二个参数的幂。 static doublerandom() 返回值为 double值为正号，大于等于 0.0 ，小于 1.0 。 static doublerint(double a) 返回与参数最接近值的 double值，并且等于数学整数。 static longround(double a) 返回参数中最接近的 long ，其中 long四舍五入为正无穷大。 static intround(float a) 返回参数中最接近的 int ，其中 int四舍五入为正无穷大。 static doublesin(double a) 返回角度的三角正弦。 static doublesinh(double x) 返回的双曲正弦 double值。 static doublesqrt(double a) 返回的正确舍入正平方根 double值。 static doubletan(double a) 返回角度的三角正切。 static doubletanh(double x) 返回的双曲正切 double值。 static doubleulp(double d) 返回参数的ulp的大小。 static floatulp(float f) 返回参数的ulp的大小。

java源码

public final class Math {

private Math() {}

public static final double E = 2.7182818284590452354;

public static final double PI = 3.14159265358979323846;

public static double sin(double a) {

return StrictMath.sin(a); // default impl. delegates to StrictMath

}

public static double cos(double a) {

return StrictMath.cos(a); // default impl. delegates to StrictMath

}

public static double tan(double a) {

return StrictMath.tan(a); // default impl. delegates to StrictMath

}

public static double asin(double a) {

return StrictMath.asin(a); // default impl. delegates to StrictMath

}

public static double acos(double a) {

return StrictMath.acos(a); // default impl. delegates to StrictMath

}

public static double atan(double a) {

return StrictMath.atan(a); // default impl. delegates to StrictMath

}

public static double exp(double a) {

return StrictMath.exp(a); // default impl. delegates to StrictMath

}

public static double log(double a) {

return StrictMath.log(a); // default impl. delegates to StrictMath

}

public static double log10(double a) {

return StrictMath.log10(a); // default impl. delegates to StrictMath

}

public static double sqrt(double a) {

return StrictMath.sqrt(a); // default impl. delegates to StrictMath

// Note that hardware sqrt instructions

// frequently can be directly used by JITs

// and should be much faster than doing

// Math.sqrt in software.

}

public static double cbrt(double a) {

return StrictMath.cbrt(a);

}

public static double IEEEremainder(double f1, double f2) {

return StrictMath.IEEEremainder(f1, f2); // delegate to StrictMath

}

public static double atan2(double y, double x) {

return StrictMath.atan2(y, x); // default impl. delegates to StrictMath

}

public static double pow(double a, double b) {

return StrictMath.pow(a, b); // default impl. delegates to StrictMath

}

public static double sinh(double x) {

return StrictMath.sinh(x);

}

public static double cosh(double x) {

return StrictMath.cosh(x);

}

public static double tanh(double x) {

return StrictMath.tanh(x);

}

public static double hypot(double x, double y) {

return StrictMath.hypot(x, y);

}

public static double expm1(double x) {

return StrictMath.expm1(x);

}

public static double log1p(double x) {

return StrictMath.log1p(x);

}

}

public final class StrictMath {

private StrictMath() {}

public static final double E = 2.7182818284590452354;

public static final double PI = 3.14159265358979323846;

public static native double sin(double a);

public static native double cos(double a);

public static native double tan(double a);

public static native double asin(double a);

public static native double acos(double a);

public static native double atan(double a);

public static strictfp double toRadians(double angdeg) {

// Do not delegate to Math.toRadians(angdeg) because

// this method has the strictfp modifier.

return angdeg / 180.0 * PI;

}

public static strictfp double toDegrees(double angrad) {

// Do not delegate to Math.toDegrees(angrad) because

// this method has the strictfp modifier.

return angrad * 180.0 / PI;

}

public static native double exp(double a);

public static native double log(double a);

public static native double log10(double a);

public static native double sqrt(double a);

public static native double cbrt(double a);

public static native double IEEEremainder(double f1, double f2);

public static native double atan2(double y, double x);

public static native double pow(double a, double b);

public static native double sinh(double x);

public static native double cosh(double x);

public static native double tanh(double x);

public static native double hypot(double x, double y);

public static native double expm1(double x);

public static native double log1p(double x);

}