How to pass a long in ...Long ll = Long.valueOf(3L);//gives

[Amit Das]

hi all,

How to pass a long in ...Long ll = Long.valueOf(3L);//gives Runtime execption(Number Format)

whereas .....Float f = Float.valueOf(3.9f); //works fine.


one more question:

How to pass a byte.......Byte b = Byte.valueOf(??);

i tried:

class KandB0 {
public static void main(String[] args) {

Float i2 = Float.valueOf("4.5");

Byte b1 = Byte.valueOf("i2.byteValue()");

System.out.println(b1);
}
}  

but i get a Number Format Exception!!!

help!!!

amit

[Simon Cockayne]

Amit,

You need to check out the constructor and conversion methods available to "wrapper" classes.

public class WrapperTest {
 
public static void main(String[] args) {

//1)
int i = 128;
Integer I = new Integer(i);

//2)
//valueOf(String x)
long l = 9999;
Long L = new Long(l);

//3)
Float F = Float.valueOf("4.5");

byte b1 = F.byteValue();
System.out.println(b1); //4
Byte B1 = new Byte(b1);
System.out.println(B1); //4
 
}}
 

Cheers,

Si.

[Amit Das]

hey Simon,

the code u've written creates a Byte object by a new operator.....seems as u've not read my question carefully!!!

well let me rephrase......the valueOf() method is a static method for the Wrapper classes and it's overloaded twice. the first one takes appropraite primitive value as a String and returns an Object of a wrapper class with string value inculcated in appropraite form....okie!!!

there is one more valueOf(), which takes two parameters....we're not into that now.....

the question is how do you pass a byte for the Byte.valueOf(???)
what do you write for ??? how to write byte value(like 2 is default int,
2.0 is default double, 2f is floating point, etc....)

one way can be : Integer i = new Integer("20");
byte b = i.byteValue();

now we can think of passing this value(which is in b) to the valueOf() as an argument.....but....that dosen't work

similar is my next question out there....

thanx
amit

[Amit Das]

Simon's

Float F = Float.valueOf("4.5")

Simon .....4.5 is a double number okie!!!

dont you think there shud be an error.....

secondly how do you pass long for Long.valueOf(3L)//gives NumberFormat Exception

[Amit Das]

sorry its Long.valueOf("3L") which gives error.....plz make a note....

[Simon Cockayne]

Amit,

I was just trying to show you some different examples.

for *wrapper*.valueOf(String)

Byte B2 = Byte.valueOf("5");

System.out.println(B2);

Cheers,

Si.

[Amit Das]

now u c ......as in your example 5 is actually an int value which you're passing...correct me if i'm wrong....my question is how do you pass a byte there....?
hope mow you'll get my point..

[Simon Cockayne]

Amit,

It is not an int or a byte...it is a String.

Byte.valueOf takes a String and turns it into a wrapper class, i.e. Byte.

Cheers,

Si.

[Amit Das]

u're right that the valuOf() method takes a String but that String is actually aupposed to be of appropriate kind of primitive value:
for eg:

Float f = Float.valueOf("3.4f"); //works
Float f1 = Float.valueOf("3.4"); //works

so when we write 3.4f and if we write 3.4 dont you think its diff???

why doesn't
Long l = Long.valueOf("3L") work??? do u have an answer for this...??

[Jay Pawar]

Amit,
You can check the Long.valueOf() implementation in Long.java file. I hope you know where this file is. In case not, it should be in the path where you downloaded the j2sdk. There is a winzip file src.zip. Just open that zip file and look for Long.java.
That will help you to understand the reason.

[prajkta patil]

hi amit,
i have some notes.i think it will definitely help u.
1]The Float constructor is overloaded: one version accepts a primitive of type float; one accepts a primitive of type double; one accepts a String representation of a floating-point literal.
2]in constructors of wrapper classes ,arguments of type String can not contain an integer type suffix, L or l. A floating-point suffix, F, f, D or d, is acceptable.
suppose,
Which of the instance creation expressions produce a run-time

error?

a. new Float('A')
b. new Float("A")
c. new Float(1L)
d. new Float("1L")
e. new Float(0x10)
f. new Float("0x10")
g. new Float("010")

ans:b,d,f
explanation:
i]The Float constructor is overloaded: one version accepts a primitive of type float; one accepts a primitive of type double; one accepts a String representation of a floating-point literal
ii]The String literals "NaN" and "Infinity" are accepted by the Float constructor. A sign (+ or -) is optional.
iii]The primitive char literal 'A' is converted to a float, and is accepted by the constructor that declares a parameter of type float.
iv]The API specification states that any other String must represent a floating-point value;
v]The leading 0 of an octal value is ignored, and the String is
parsed as a decimal value. A String representation of a hexadecimal
value is not acceptable.
vi]The String "A" does not represent a floating-point literal
value; therefore, a NumberFormatException is thrown.
vii]Arguments of type String can not contain an integer type suffix, L or l. A floating-point suffix, F, f, D or d, is acceptable, but the suffix has no impact on the result.
i think this much is sufficient to clear ur first doubt.
now i am thinking about second.

[prajkta patil]

same rules r applied for valuOf method only difference is that value of method takes String or wrapper class objects not primitives.

[Amit Das]

thanx Prajakta,

ur explanation is helpful....

[Animesh Shrivastava]

How to pass a byte.......Byte b = Byte.valueOf(??);

i tried:

  
class KandB0 {
    public static void main(String[] args) {
Float i2 = Float.valueOf("4.5");
Byte b1 = Byte.valueOf("i2.byteValue()");
System.out.println(b1);
   }
}  
 

Look at the code what u r trying to do,
u r passing a string "i2.byteValue()" in the argument to Byte.valueOf(), and its quite obvious that it has to throw error.

How to pass a long in ...Long ll = Long.valueOf(3L);//gives Runtime execption(Number Format)

whereas .....Float f = Float.valueOf(3.9f); //works fine.

Thats because the method valueOf() has been implemented differently in the Float class. It can accept f or d as its suffix. So thats how it is. But in the case of Long's valueOf(), its implemented as
"new Long(Long.parseLong(s))" So that throws an error.