Require help in type casting concept

[Deepakk Verma]

Hello to all Ranchers,
I have been working on this small practice program where i got stuck. This is a simple program on the type casting concept..here i am getting a error as

try12.java:17:possible loss of precision
found :int
required:short

the code is as follows:

public class try12 
{
	public static void main(String args[])
	{
		int lightspeed;
		short time;
		short days;
		short seconds;
		long distance;
		lightspeed = 186000;
		
		days = 1000;
		
		time = 32767;
		
		seconds = days * time;
		System.out.println(seconds);
		
		int second = days * time;
		System.out.println(second);
		
		distance = lightspeed * seconds;
		System.out.print("In "+ days);
		System.out.print(" days light will travel about ");
		System.out.println(distance + " miles.");
	}
}

But then i type casted it and compiled it i got the result as

=============================================================
-1000
32767000
In 1000 days light will travel about -186000000 miles.
=============================================================

Now i dont understand from where did this -1000 came from

public class try12 
{
	public static void main(String args[])
	{
		int lightspeed;
		short time;
		short days;
		short seconds;
		long distance;
		lightspeed = 186000;
		
		days = 1000;
		
		time = 32767;
		
		seconds = days * time;
		System.out.println(seconds);
		
		int second = (short)(days * time);
		System.out.println(second);
		
		distance = lightspeed * seconds;
		System.out.print("In "+ days);
		System.out.print(" days light will travel about ");
		System.out.println(distance + " miles.");
	}
}

please tell me how this seconds = -1000 is evaluated
Thanking you
Deepak Verma

[Greg Stevens]

Try this to see the difference:

  
public class try12 
{
	public static void main(String args[])
	{
		int lightspeed;
		short time;
		short days;
		short seconds;
		long distance;
		lightspeed = 186000;
		
		days = 1000;
		
		time = 32767;
		
		seconds = (short) (days * time);
		System.out.println("seconds: " + seconds);
		
		int second = days * time;
		System.out.println("second: " + second);
		
		distance = lightspeed * seconds;
		System.out.print("In "+ days);
		System.out.print(" days light will travel about ");
		System.out.println(distance + " miles.");
	}
}  

"seconds" is assigned the result of casting (days * time) to a short. Since (days * time) is larger than the maximum allowed value for a
short (32,767), the value does not fit properly in the short variable and doesn't make any sense (-1000).

The int variable "second" is assigned the result of integer arithmetic (days * time) and so the value is 32767 * 1000 = 32,767,000.

[Henry Wong]

try12.java:17:possible loss of precision
found :int
required:short

This means that you have an assignment that the compiler can't determined to be safe -- meaning that the value being assigned may exceed the range of the target.

To avoid this, you casted it... however, in this example, the value did exceed the range of a short. A casting operation from an int to a short, merely truncates the int -- meaning only the lower bytes will be used.

And the reason the value is negative is because this "overflow" happened to overflow into the sign bit.

Henry

[Ruben Guillen]

Please also give a look to the following reference from

Java Language Specification Third Edition

4.2.1 Integral Types and Values
The values of the integral types are integers in the following ranges:

For byte, from -128 to 127, inclusive
For short, from -32768 to 32767, inclusive
For int, from -2147483648 to 2147483647, inclusive
For long, from -9223372036854775808 to 9223372036854775807, inclusive
For char, from '\u0000' to '\uffff' inclusive, that is, from 0 to 65535