how can we use math .pi without using impot java.lang.Math*;

PROGRAMING LANG:- JAVA

You can...
import static java.lang.Math.PI; and refer to it as PI
or
don't use an import and refer to it as java.lang.Math.PI in your code.

Why???

example of how to use Math.PI:
/
System.out.println(5
Math.PI);
*/

you don't even need to import the java.lang.Math.* thing.