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javamathimportstaticpi

Importing Math.PI as reference or value

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:

 public class Circle {
     static double getCircumference(double radius ) {
          return PI * 2 * radius;
     }
     public static double getArea(double radius) {
          return PI * radius * radius;
     }
}

Which import statement will enable the code to compile and run?

import java.lang.*;

import static java.lang.Math.PI;

import java.lang.Math.*;

import java.lang.Math;

I answered import static java.lang.Math.PI;

BUT the explanation of two other options below confuses me:-

The statements import java.lang.Math; and import java.lang.Math.*; will not enable the code to compile and run. These import statements will only allow Math.PI as a reference to the PI constant.

My question is: what would be wrong with the import statements only allowing a reference to the PI constant? Would the value be uninitialized and zero?

Solution

  • '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.