为什么双倍宽度= 50/110000;输出是0.000000000000000？

Question

This is my code :

double width = 50/110000;
System.out.println("width ori is "+width );

And the output is: 0.00000000000

What's wrong ? the expected output has to be 4.5454545454545455E-4

Any body can explain to me why?

Answer 1

Because you're dividing two integers, so it will only take the integer part (integer division).

Dividing integers in a computer program requires special care. Some programming languages, treat integer division (ie by giving the integer quotient as the answer). So the answer is an integer.

Examples :

In real life                  In Java

4/3  = 1.33333                4/3  = 1
25/12 = 2.083333              25/12 = 2
9/2 = 4.5                     9/2 = 4
50/110000 = 0.000454545       50/110000 = 0

You can cast one of the number (or both but it's actually useless) to double to avoid that :

double width = (double)50/110000;
double width = 50d/110000;
double width = 50.0/110000;

Answer 2

Result of int/int returns you an integer .

So the decimal part got truncated resulting you with an integer

You need to cast:

double width = (double)50/110000;

As @Josh M has pointed, You can also try :

double width = 50d / 110000d;

Answer 3

Explanation to what's happening:

In Java, the default type of numbers is int , so when you write 50/110000 , they're both considered int , although you defined the result to be double .
When int division occurs, the result will be 0 , because they are both int s, then the double will hold this value, which will be represented as double , so you're getting 0.000000 .

Possible solutions:

• Coding these numbers with d : 50d/110000d .
• Casting one side explicitly (the other will be implicitly cast): (double)50/110000 .
• 50.0/110000 .

See Chapter 5. Conversions and Promotions , it'll really help you.