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I have a question about primitive variable types. How come whenever I declare a long variable, I have to put an "l" at the end of the value or else I get a compiler error saying "integer number too large."? It also happens with doubles, too.

And I have another question about "double" variable types. How come the Java documentation thing lists them as being able to hold values from "8 bytes IEEE 754. Covers a range from 4.94065645841246544e-324d to 1.79769313486231570e+308d (positive or negative)." But when I put in a higher value, even something (relatively) small like two billion won't fit unless I put a "d" at the end of the value. Why is this? And what does the "-324d" and "+308d" thing mean? Is this scientific notation or is that the decimal precision of the "double" variable type? Thanks.

Zeus · Accepted Answer

for normal int initialization like
int a = 9 (9 would be treated as int type)
int a = 9L (9 would be treated as long type)

the truth applies to the relation between floating point and double.

int -> 32 bits; 
long -> 64 bits;

float -> 32 bits;
double  ->64 bits;

for all of the primitive data types, length to store the value is calculated during compile time.

Thats why java need to know whether it is a int or long; float or double.

For Object data type, during the compile time, a length of space used is calculated for the reference only, not the actual value.

4.0454545e-324d means 4.0454545 * (10)^-324

10^2 means 10 power 2

4.05e-2d means 0.0405

The d denotes that the whole value 4.4343..... is a double, not refers to 324 only.

:) good question !

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