Java

Question

What is the output of this program?
 

class Conversion {
    public static void main(String args[]) 
    { 
        double a = 295.04;
        int b = 300;
        byte c = (byte) a;
        byte d = (byte) b;
        System.out.println(c + " " + d);
    } 
}

a) 38 43
b) 39 44
c) 295 300
d) 295.04 300

Answer 1

b) 39 44
 

PS: This is Java code and the rules of Java do not apply to C/C++.

Byte data type being of 8 bits can hold only 256 unique values.

Hence during type casting value changes. For integer the lowest 8 bits is assigned to byte, and for double/float the lowest 8 bits of its integer part is assigned to byte. One more thing is in Java, this type conversion is not IMPLICIT and without being explicity type casted if we assign a higher type to a byte, COMPILE ERROR results (but we can assign a lower sized variable to a higher sized one like int a = b; where b is a byte). Here, we get the following result:

c = a mod 256 = 39 (taking the lowest 8 bits)

d = b mod 256= 44 (taking the lowest 8 bits from the corresponding integer representation)

PS: In Java there is no concept of unsigned and hence for a byte, if the MSB is 1, it becomes negative (2's complement representation). This is similar to "signed char" in C.

Comments

Thank you shubhi mam for the answer.

you explained so lucidly and i understood i was earlier searching this answer on google it was written in very tough language and was not able to understand.

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But please tell from where does this 256 arised ?

i mean why only a mod 256 

and b mod 256 ?

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Byte can hold data values from -128 to 127 those are 256 numbers .

-128 to -1	128 values
0	1 value
1 to 127	127 values

Thus total 256 values.
In other words the capacity of byte is 256. Hence we take a mod 256. 

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Thank you so much mam now i understood completely. you are best in java . claps for you mam touches your feet!

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suppose in the Question

if we take two variable of type int

and then type cast into int 

(just reverse of this given question )

then how we would solve please tell that also ??

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This is another question . Please tell how to solve this ?

class Value 

{

       public static void main(String [] s )

     {

     int i = 255;

byte b=(byte)i ;

char c = (char)b;

System.out.println("int value of char : " + (int) c);

}

}

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Firstly, I believe , you are stuck with the number '256'.

Try to see the concept. Consider int and byte . Consider the following table.. see what int values will look like when converted to byte. (Byte range of nos is -128 to 127)

Int Values	Byte Values
0	0
110	110
127	127
128	-128
129	-127
130	-126
255	-1
256	0

Understand it like a mapping of numbers, Now when you give any number greater than 255 the pattern repeats .. so you can take mod 256. and then knowing the pattern above you can get the byte value.
I hope this clears the byte value conversion.

So byte b = (byte) i , after this b =-1 as i =255.

Now coming to the char conversion, in Java , char is 16 bit unicode. Moreover char is unsigned so that gives you a possible range of values from 0 to 65535 
so char c = (char) b , will convert it to unicode representation. Unicode values are from 0 - 65535. By the same logic as we used for byte represenation , -1 value of byte will be 65535 in char.

 when u execute

System.out.println("int value of char:" + (int) c);

The value 65535 will be printed.

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I suggest you go through Oracle javadocs for getting the basics of data types cleared.They are the best source to resolve any query.

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mam i understood what you are trying to say , 

but please tell any genralized trick to solve.

like for the values 129  , 130 and 255 how we will get the respective byte values ? 

Integer	Byte
129	-127
130	-126
255	-1

Suppose there is some other integer value which is large or small then how we will get the respective byte value? 

Like for 300 we re doing 300 modulo 256 then answer is 44

but when we re doing 130 modulo 256 then answer is 130  which does not produce -1 

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You are trying to say whatever i understood i did the mapping with my own pen and copy and i m understanding you what you are trying to say. But please tell me how to get the number -127, -126 , -1 for the respective integer value of 129,130 and 255.

I mean to say any gnerealized trick to get these numbers ?

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With your last query , I understand I have drastically failed to explain the concept and I intend no trick. 

I hope someone better can step up and explain the same. 

I suggest you re-post your query as a new question and hopefully both of us will get a better explanation.

NOTE: IMPORTANT! Always refer to Oracle javadocs for authentic information.

 

 

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See mam i understood the mapping perfectly.

No doubts in that explanation but in this way if i will calculate then it will take 15 minutes to get the exact value in bytes mam . am i right or wrong ????

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I am afraid there is no formula for this as such. But even if you solve it with logic it would hardly take 2 mins. But because you are so pertinent to make formula for this, let's make one then. 

Let X be the int no to be converted to byte. Let it's byte representation be B.

If 0 <= X <= 127  then B = X.

If 128 <= X <= 255 then , 

let p = X - 128

B = -128 + p

Now if X > 255 
Take X mod 256 , you will get a number between 0 and 255 (both inclusive) . then you can apply the above formula to get the value B.

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 Yes mam now i m fully satisfied with the answer and the logic .  

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so char c = (char) b ,

how you are mapping this ? please tell mam i beg you please explain this also ? just last step ??

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With some genralized trick so that i can solve and convert any given byte type number into respective characater type .

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?????????????????

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@Alok When in a community show respect to others. So, please don't

1. beg for answers
2. put "important" in title

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sir bygod i always give respect.

whenever i talk with u or anyone else also then also i call him or her as mam or sir.

you are blaming me for no reason and putting taunts to me

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I was not blaming you - there are many people who thinks calling "mam" or "sir" is respect. We in India always do that to teachers. But actual respect is in doing what the teacher says and not doing the opposite and just calling "sir" or "madam". In top institutes like IISc, some students call professors by first name and this is the standard in developed countries also.

Anyway by respect I meant that you should not disturb others - especially those who answer you. Every one here want answer to their queries- but answering takes a lot of time as this is not history or literature where answers can be just written without thinking. I just edited the answer to this question - it took me more than 15 minutes to do so because I had to write, compile, test and then to write. Did you try compiling before posting the question? If not you are never going to understand the solution however someone explains it. Someone can feed you some tricks which works for many cases, but will fail when someone sets question properly as in GATE.  

I can answer this question better- but currently you won't get it - because you are looking for tricks. To answer this your mind should work like a compiler which requires proper knowledge of language semantics. Then after each line you can know the possible values and answer any question of this type.

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Thanks Arjun for the edit .Now the answer is more sound and strong.