试图在Java中找到长数据类型的范围

Question

trying to verify range of long in java.. why is this program not working? it gives infinite loop (probably). i'm not getting output at the command line and the cursor keeps blinking.

class range
{
public static void main(String [] args)
{
         long i;
     for(i=0;;i++)
    {
         long c= (long)(i+1);
         if(i>c)    //upper_limit+1=lower_limit
            break;  // hence, at i=upper_limit c(=i+1) < i

    }
    System.out.println("upper ="+i);
    for(i=-1;;i--)
    {
        long c=(long)(i-1);         
        if(i<c)             //lowerlimit-1=upperlimit
            break;          //hence at i=lowerlimit c(=i-1)>i
    }
    System.out.println("lower ="+i);
}
}

Answer 1

Your program will work eventually - but it's got to perform 2 ⁶³ iterations (in each direction) first. That's going to take a very long time. Long.MAX_VALUE and Long.MIN_VALUE are rather simpler ways of finding this out. Or just look at JLS 4.2.1 :

The values of the integral types are integers in the following ranges:

• ...

• For long , from -9223372036854775808 to 9223372036854775807, inclusive

If you want to see your program finding the right values, just start it closer to the final result:

for(i=Long.MAX_VALUE - 10;;i++)
...
for(i=Long.MIN_VALUE + 10;;i--)

That quickly ends with output of:

upper =9223372036854775807
lower =-9223372036854775808

Answer 2

Why do you think your program is not correct? It simply will take a long while - until long overflows(about 2^63 iterations). I suggest that you use Long.MIN_VALUE and Long.MIN_VALUE or if you want to avoid this solution use binary search for when overflow happens.

Also you may consider using the same program for short to verify it is correct, simply very time consuming.

Answer 3

You can use Long.MAX_VALUE and Long.MIN_VALUE

It will take lots of time to enumerate all 2^64 possible long values

Answer 4

There is no reason to start at 0 or -1.

If you want to verify MIN/Max values, try it like this:

class range
{
public static void main(String [] args)
{
         long i;
     for(i=Long.MAX_VALUE;;i++)
    {
         long c= (long)(i+1);
         if(i>c)    //upper_limit+1=lower_limit
            break;  // hence, at i=upper_limit c(=i+1) < i

    }
    System.out.println("upper ="+i);
    for(i=Long.MIN_VALUE;;i--)
    {
        long c=(long)(i-1);         
        if(i<c)             //lowerlimit-1=upperlimit
            break;          //hence at i=lowerlimit c(=i-1)>i
    }
    System.out.println("lower ="+i);
}
}