1 public class MathDemo {
 2     public static void main(String[] args) {
 3 
 4         double tan = Math.tan(Math.PI * 45 / 180); // 求角度的tan
 5         double aa = Math.atan(1) * 180 / Math.PI;// 根据tan求角度
 6         double degrees = Math.toDegrees(Math.PI);// 根据弧长求角度
 7         double radians = Math.toRadians(180);// 根据角度求弧长
 8         System.out.println(tan);
 9         System.out.println(aa);
10         System.out.println(degrees);
11         System.out.println(radians);
12     }
13 
14 }