The java.lang.Math class of common Java APIs (with analysis and examples) _01

The Math class directly inherits the Object class:

public final class Math extends Object

Math 类包含用于执行基本数学运算的方法，如初等指数、对数、平方根和三角函数。java.lang包内有一个名为StrictMath类，StrictMath类和Math类有很多同名方法。在默认情况下，很多 Math 类方法直接调用 StrictMath中的等价方法来完成。

为了确保 Java 程序的可移植性，StrictMath类中的函数根据fdlibm（免费发布的数学库）定义，在不同平台执行都能获得完全一样的结果，多次运行也能产生一样的结果。Math类不像StrictMath类那样严格，允许浮点数最后一两个位数有误差，以此换来性能的提升。

Compare the source code of the Math class with the source code of the StrictMath class

StrictMath class:

public final class StrictMath
{
    public static native double sin(double a);//The method modified by native is called a native method, which is implemented by non-Java code (such as C language code).
}

Math class:

public final class Math
{
    public static  double sin(double a)
    {
        return StrictMath.sin(a);
    }
}

So if you want better performance, use the Math class (the Math class is more common); but in some cases, it is more important to get a completely reliable and predictable result, then you have to use the StrictMath class.

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Let's enter the topic below and list the more commonly used Math class APIs.

Note: The fields and methods in the Math class are static, that is, there is no need to create an object when calling, just call Math.xxx directly.

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static domain
Math.E	e: base of natural logarithm, double type. 2.718281828459045
Math.PI	π: The ratio of the circumference of a circle to its diameter, double type. 3.141592653589793

static method
static double abs(double a)	Returns the absolute value of a. Example: abs(-4.3) = 4.3
static double cos(double a)	The argument is an angle in radians, and the cosine of that angle is returned. 例： cos (Math.PI) = -1
static double sin(double a)	The argument is an angle in radians, and the sine of that angle is returned . 例： sin (Math.PI / 2) = 1
static double tan(double a)	The argument is an angle in radians, and the tangent of that angle is returned . Example: tan (Math.PI / 4) = 1
static double atan2(double y, double x)	Convert rectangular coordinates (x, y) to polar coordinates (r, theta), returning the resulting angle theta. Game design uses a lot. Example: atan2 (1,1) = 45
static double ceil(double a)	Returns the smallest integer greater than or equal to a, ie rounded up. Example: ceil(11.8) = 12, which can be understood as the ceiling.
static double floor(double a)	Returns the smallest integer less than or equal to a, ie rounded up. Example: ceil(11.8) = 11, which can be understood as the floor.
static double exp(double a)	返回自然数 e 的 a 次幂的值。例：exp(2) = Math.E * Math.E
static double log(double a)	返回 a 的自然对数（即底数是 e）。例：log(Math.E * Math.E) = 2
static double log10(double a)	返回 a 的底数为 10 的对数。例：log10(100) = 2
static double max(double a, double b)	返回两个 a、b 中较大的一个。例：max(5.7, 6,3) = 6.3
static double min(double a, double b)	返回两个 a、b 中较大的一个。例：min(5.7, 6,3) = 5.7
static double pow(double a, double b)	返回 a 的 b 次方。例：pow(2,3) = 8
static long round(double a)	返回最接近 a 的整数。可用于四舍五入。例：round(3.3) = 3
static double signum(double d)	返回参数的符号函数；例：signum(0) = 0; signum(0.01) = 1; signum(-0.01) = -1;
static double sqrt(double a)	返回的 a 的正平方根。例：sqrt(4) = 2
static double toDegrees(double radians)	将用弧度表示的角转换为近似相等的用角度表示的角。例：toDegrees(Math.Pi) = 180
static double toRadians(double degrees)	将用角度表示的角转换为近似相等的用弧度表示的角。例：toRadians(180) = Math.PI

The java.lang.Math class of common Java APIs (with analysis and examples) _01

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