Public class mathtest {public static void main (string [] ARGs) {// todo auto-generated method stub // math. round (): Rounding system. out. println ("1. the first digit after the decimal point = 5 "); system. out. println ("positive number: math. round (11.5) = "+ math. round (11.5); system. out. println ("negative number: math. round (-11.5) = "+ math. round (-11.5); system. out. println ("2. the first digit after the decimal point <5 "); system. out. println ("positive number: math. round (11.49) = "+ math. round (11.49); system. out. println ("negative number: math. round (-11.49) = "+ math. round (-11.49); system. out. println ("3. first digit after decimal point> 5 "); system. out. println ("positive number: math. round (11.69) = "+ math. round (11.69); system. out. println ("negative number: math. round (-11.61) = "+ math. round (-11.69); system. out. println ("Summary: if a positive number is greater than 5 after the decimal point, it is rounded off. If a negative number is greater than or equal to 5 after the decimal point, it is rounded off."); system. out. println ("That is to say, after the decimal point is greater than 5, all plus, equal to 5 plus, less than 5 do not add ");}