Importing Math.PI as reference or value

Question

I\'m preparing for a basic certification in Java.

I\'m a little confused by the answer to a question that I have got right(!):-

Given:

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Answer 1

'Allow Math.PI as a reference to the PI constant' means that your code will have to look like this in order to work:

static double getCircumference(double radius ) {
      return Math.PI * 2 * radius;
 }
 public static double getArea(double radius) {
      return Math.PI * radius * radius;
 }

What import java.lang.Math; does is importing the class java.lang.Math so you can reference it with Math instead of the qualified version java.lang.Math. import java.lang.Math.*; does the same for Math and all nested classes, but not it's members.

Answer 2

This

import java.lang.Math.*;

imports all (accessible) types declared within Math.

This

import java.lang.Math;

is redundant because Math is part of java.lang which is imported by default.

Both will require that you use

Math.PI

to access the field.

This

import static java.lang.Math.PI;

imports the static member Math.PI so that you can use its simple name in your source code.