Double instance variables in java

Question

Why do double instance variables in java have a lower case d attached to them? Do they need to have this?

Example:

double area = 0d;
double avgDailyTemp = 26d;

etc...

Answer 1

A number literal by default is an integer. If you attempt to pass a number like ten billion into Java double it'll error since it's outside the bounds of an integer. Specifying the lowercase d explicitly defines it as a double literal instead.

Answer 2

double a = 10000000000; // ERROR! Integer number too large 
double b = 10000000000d; // OK!

Answer 3

没有d的数字0和26是int值。

Answer 4

It is not the variable which requires the d , but the constant value declared. It is a "hint" to the compiler of the data type.

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html