kevinn lee

thanks henry

class Outer { public Object innerCls(){ class Inner{ } return new Inner(); } public static void main(String[] args){ Outer out=new Outer(); Object o=out.innerCls(); System.out.print(o); //Outer.Inner k=o; } }

output
Outer$1Inner@19821f

what type of referrence variable can refer to "o" other than Object type?
thanks

thank you sahil

class Forr{ public static void main(String[] args){ int i=0; for ( i=0,int j=90; i<j; i++) { j--; } } }
why doesent compiler allow to use a pre declared variable and a variable declared within the for loop together?
code compiles when both are declared within and when both are declared out of the loop.
or is it because line "i=0,int j=90;"it self is faulty when taken alone?

thanks

http://java.sun.com/docs/books/tutorial/java/nutsandbolts/variables.html
according to this document

Subsequent characters may be letters, digits, dollar signs, or underscore characters.

"#" is not a letter,digit,dollar sign or an underscore.Thats why your identifier is illegal.

Henry Wong wrote:

kevinn lee wrote:
why doesnt line 1 one causes a runtime exception while line 2 does?

The answer to "why" is probably lost in the bowels of history -- ie. I doubt if anyone knows. These are merely two different implementations. The Float implementation seems more robust, can deal with extra whitespaces, and follows the same definition of floating point as the JLS. However, the Long implementation seems to be less robust, and can only take digits -- no white space, no leading zero for octal, no hexidecimal syntax, etc.

Maybe they were done at different times. Maybe they were done by two different developers. Etc. Your guess would probably be as good as mine.

Henry

thank you henry

I came across this in a certain mock exam.Are we supposed to know things like this for the exam?

class TestFloatConstructors{ public static void main(String args[]){ Float f1=new Float(23.5f); Float f2=new Float(23.5); Float f3=new Float("23.5f");//1 Float f4=new Float("23.5"); Float f5=new Float("012.5"); Long l=new Long("52L");//2 System.out.print(f1+" "+f2+" "+f3+" "+f4+" "+f5); } }
why doesnt line 1 one causes a runtime exception while line 2 does?
thanks

Thanks a lot Henry

but at runtime isnt it the same String literal "abc" that lies in the String pool that both s5 and s3 are pointing to?

class TestString{ public static void main(String args[]){ String s1="abc"; final String s2="ab"; String s3=s2+"c";//1 String s4="ab";//2 String s5=s4+"a"; System.out.println(s1==s3); System.out.println(s1==s5); } }
can someone explain the reason for the two different outputs?what difference does s3 have because s2 is final?
thanks.

thanks a lot sandra

Jim Hoglund wrote:The string pool mechanism is at work here. To conserve memory, the compiler will
at times, share a string object if sX.equals(sY). Apparently in your case it put "abc" in
the pool and used it again. (Maybe for s1, s3 and s4).)

Jim ... ...

but it seems as if "abc" is not shared here since "s1==s3" turns out to be false.
thanks

Sandra Bachan wrote:Hello,

hello
go to the link given by Ravinderjit
it explains what is special about Strings
thanks for replying

Ravinderjit Singh wrote:Because String s3=s2+"c";//1 will create a new String object, means s1 and s3 are referring to two different objects.

you mean

String s3=s2+"c";

is like
s3=new String("abc");
rather than
s3="abc";
is it?
thanks

compiler compiles any code unless it knows exactly that the particular casting is impossible.
In your case there can be a class which implements both the interfaces.Then both i1 and i2 can refer to an object of that class and the casting between I1 and I2 makes sense.

class TestString{ public static void main(String args[]){ String s1="abc"; String s2="ab"; String s3=s2+"c";//1 String s4="abc"; System.out.println(s1==s3);//2 System.out.println(s1==s4); } }
why doesnt line 2 give "true"?I mean after line 1 doesn't s3 refer to the same string literal "abc" in String constant pool that s1 is refering to?
Or is there a different mechanism how a new String is created when "+" operator is used.Please explain.
thanks