JAVA实现快速傅里叶变换FFT功能，实数和复数都可以实现傅里叶变换-JAVA Fast Fourier Transform FFT functions, real and complex Fourier transformation can be achieved

使用了apache自带函数包实现傅里叶变换，返回的是一个复数数组(The use of Apache comes with the function package to achieve the Fourier transform, returns a complex array)