http://www.java2s.com/Code/Java/Data-
Type/Obtainingtheintegerandfractionalparts.htm

double num;
long iPart;
double fPart;

// Get user input
num = 2.3d;
iPart = (long) num;
fPart = num - iPart;
System.out.println("Integer part = " + iPart);
System.out.println("Fractional part = " + fPart);

输出：

Integer part = 2
Fractional part = 0.2999999999999998