Create a new Java class called 'Circle' with the following attributes:

$-$ A private variable for 'diameter'

$-$ A public method called getDiameter$()$

$-$ A public method called setDiameter$()$

$-$ A public method called getArea$()$

$-$ A public constructor that takes a single parameter $($diameter$)$

$-$ A public constructor that takes no parameters $($defaults diameter to $"1")$