Wrapper-Q

[Vishnu Prakash]

  public class Test041
{ 
static double d;
static float f;
 
public static void main(String args[])
{ 
compare(Long.MAX_VALUE, Long.MAX_VALUE );
compare(Integer.MAX_VALUE, Integer.MAX_VALUE );
compare(Character.MAX_VALUE, Character.MAX_VALUE);
compare(Short.MAX_VALUE, Short.MAX_VALUE );
compare(Byte.MAX_VALUE, Byte.MAX_VALUE ); 
}
static void compare(double d, float f)
{
if (f == d) System.out.print(" equal" );
else System.out.print(" unequal"); 
} 
}

Q: Why Integer.MAX_VALUE is not returning equal.

[Mike Gershman]

Integer.MAX_VALUE has 31 bits of precision plus a sign.

A 32 bit float has 8 bits for the exponent, 23 bits for the fraction, and a sign bit. So a float loses precision (not magnitude) in the conversion from a 31 bit value.

A 64 bit double has 11 bits for the exponent, 52 bits for the fraction, and a sign bit. So double can hold a 31 bit value with no loss of precision.

Comparing an approximate number to an exact number, we get an unequal result.

[Rituparno Pal]

Dear Mike
If your Logic is fitting in this case tehn, why do the same thing is not happening for Long.MAX_VALUE

[Mike Gershman]

Dear Rituparno:

Thanks for your excellent question. And I thought young'uns today didn't care about bits and bytes.

Please first run the following enhancement to Vishnu's program and examine the results:

public class Test041
{ 
static double d;
static float f;
 
public static void main(String args[])
{ 
compare(Long.MAX_VALUE, Long.MAX_VALUE );
 
compare(Integer.MAX_VALUE, Integer.MAX_VALUE );
compare(Character.MAX_VALUE, Character.MAX_VALUE);
compare(Short.MAX_VALUE, Short.MAX_VALUE );
compare(Byte.MAX_VALUE, Byte.MAX_VALUE ); 
System.out.println();
 
System.out.println( Integer.toBinaryString( Integer.MAX_VALUE ) );
System.out.println( Long.toBinaryString( Long.MAX_VALUE ) );
System.out.println();
 
System.out.println( Integer.toBinaryString(Float.floatToIntBits((float)Integer.MAX_VALUE ) ) + "(float)int"  );
System.out.println( Long.toBinaryString(Double.doubleToLongBits((double)(float)Integer.MAX_VALUE ) ) + "(double)(float)int" );
System.out.println( Long.toBinaryString(Double.doubleToLongBits((double)Integer.MAX_VALUE ) ) + "(double)int" );
System.out.println();
 
System.out.println( Integer.toBinaryString(Float.floatToIntBits((float)Long.MAX_VALUE ) ) + "(float)long"  );
System.out.println( Long.toBinaryString(Double.doubleToLongBits((double)(float)Long.MAX_VALUE ) ) + "(double)(float)long" );
System.out.println( Long.toBinaryString(Double.doubleToLongBits((double)Long.MAX_VALUE ) ) + "(double)long" );
}
static void compare(double d, float f)
{
if (f == d) System.out.print(" equal" );
else System.out.print(" unequal"); 
} 
}

Integer.MAX_VALUE comes out differently when it is first converted to a float and then to a double than when it is converted directly to a double. This is because it must be rounded from 2147483647 to 2147483648 to fit in a float and the rounded value is then converted exactly to a double. However, any int can be exactly converted into a double without rounding. So we are comparing 2147483648 to 2147483647.

Long.MAX_VALUE is rounded from 9223372036854775807 to 9223372036854775808 when converted to either a float or a double. The rounded value converts exactly from a float to a double, without further rounding. So Long.MAX_VALUE comes out the same, whether converted directly to a double or converted to a float and then to a double.

Please feel free to study the bit representations and compare them to whichever write-up on IEEE 754 floating point format you prefer. Or ask another question - someone is always in the Big Moose Saloon.

Mike

[Rituparno Pal]

Dear Mike
Thanks very much for you reply. That was real beauty to discover the bit n byte stuffs.
Rituparno

[ankur rathi]

Mike the first post is clear but second one ( long one ) is not clear .
can you put some more light on this .

thanks .

[Mike Gershman]

Please run the code I provided, examine the output, then ask me a question and I'll do my best to explain.

[Mohammed Al-Qaimari]

I beleive you know that it's better to take 311-055 exam if you have 6-12 months of experience in Tiger.

I've been working with tiger since it's first beta release and I find the exam objectives challanging.
[ January 05, 2005: Message edited by: Mohammed Al-Qaimari ]