toDouble 
  Returns this number as Double.
Calling from Kotlin
Here's an example of calling this function from Kotlin code:
val actual: Double = Zero()
    .toDouble()
val expected = 0.0
assertEquals(expected, actual)Content copied to clipboard
Calling from Java
Here's an example of calling this function from Java code:
final double actual = new Zero()
        .toDouble();
final double expected = 0.0;
Assertions.assertEquals(expected, actual);Content copied to clipboard