Question 9, Chapter 6 in K&B

[sridhar row]

Which will compile and run without exception? (Choose all that apply.)
A. System.out.format("%b", 123);
B. System.out.format("%c", "x");
C. System.out.printf("%d", 123);
D. System.out.printf("%f", 123);
E. System.out.printf("%d", 123.45);
F. System.out.printf("%f", 123.45);
G. System.out.format("%s", new Long("123"));

Answer given: A,C,F and G.

Can someone explain why and how A and G are correct?

[Irina Goble]

See java.util.Formatter:

'b', 'B' - If the argument arg is null, then the result is "false". If arg is a boolean or Boolean, then the result is the string returned by String.valueOf(). Otherwise, the result is "true".

's', 'S' - If the argument arg is null, then the result is "null". If arg implements Formattable, then arg.formatTo is invoked. Otherwise, the result is obtained by invoking arg.toString().

The A is a little bit confusing as a Boolean(String) constructor will return true only for a string "true" (ingnoring case). At least they agree on null.
[ April 13, 2008: Message edited by: Irina Goble ]

[sridhar row]

Thanks Irina ..yeah i found this a little strange. Probably take sometime to sink in.

[Dinesh Tahiliani]

'b', 'B' - If the argument arg is null, then the result is "false". If arg is a boolean or Boolean, then the result is the string returned by String.valueOf(). Otherwise, the result is "true".

's', 'S' - If the argument arg is null, then the result is "null". If arg implements Formattable, then arg.formatTo is invoked. Otherwise, the result is obtained by invoking arg.toString().

Can you please explain me these lines with help of example. i am not getting it...

[Dinesh Tahiliani]

Why not b is executed , it is looking for character which we have passed ie. "x". Can some one expalin me this

[Ali Khalfan]

"X" is a string not a character...it can't be handled. 'x' could be

[Irina Goble]

Dinesh, you can use the example from the first post. Try to compile it and see what happens.

[Siri Naray]

I am still not understanding why A is right. Can anyone pl explain when %b is true or false??

[sweety sinha]

why can't option D is right? i didn't get the option A and G.
please if anyone can explain

[Siri Naray]

G is correct because when you pass new Long("123"), System.out.format evaluates new Long("123").toString()

Remember:
%s
if argument is null, result is null.
if argument is a primitive type , result=primitive
if argument is a string, result=string
if argument is an object, result=object.toString().

[Nabila Mohammad]

Originally posted by Sirishaaaaa Ghatty:
I am still not understanding why A is right. Can anyone pl explain when %b is true or false??

Any non null value will return true.