why char c='\u000a'; is not compiling?

[prem sagar bojja]

Hello friends,
Can any body explain me what's wrong with the following program..
public class CharTest {
public static void main(String[] args) {
char c='\u000a';
}
}

gives the error message: invalid character constant.
if char c='\u000d' aslo shows the same error message..
but when the statements
char c='\u000b';
char c='\u000c';
char c='\u000e';
char c='\u000f';
are compiling well..please some body help me in explaining this. Thanks inadvance..

[Ulf Dittmer]

That character happens to be the newline character, which is not allowed as per the Java Language Specification.

[prem sagar bojja]

Ulf Dittmer,
Thanks for the reply.
But can you please explain it indeatail?.. when assigned value '\u000a' to 'char c' becomes newline characher, it should not allow the code char c='\n'; to be compiled...Please explain..

[Jesper de Jong]

Unicode escape sequences like \u000a are replaced by the actual characters they represent before the Java compiler does anything else with the source code. So the \u000a in your source code is replaced internally by a linefeed character. Note that this happens before the compiler actually reads and interprets your source code. After doing this, your program looks like this.

public class CharTest {
public static void main(String[] args) {
char c='
';
}
}

That's not a valid Java program, so the compiler complains.

You can't use Unicode escape sequences in this way to insert special characters like linefeed in your application. Instead of \u000a, use \n for linefeed (or \r for carriage return).

public class CharTest {
public static void main(String[] args) {
char c='\n';
}
}

[Raghavan Muthu]

Thats because of the Unicode escapes happening before the compilation.

Jesper's explanatino would really help you. To know more about this, please have a look at here.

[Burkhard Hassel]

Howdy ranchers,

you may find it interesting that these "forbidden chars" don't even compile in a comment:

public class Trap {
public static void main(String args[]) {
// a comment that doesn't compile '\u000a'
System.out.println("ready");
}
}

this class does not compile.


Yours,
Bu.

[Raghavan Muthu]

Originally posted by Burkhard Hassel:
Howdy ranchers,

you may find it interesting that these "forbidden chars" don't even compile in a comment:

public class Trap {
public static void main(String args[]) {
// a comment that doesn't compile '\u000a'
System.out.println("ready");
}
}

this class does not compile.


Yours,
Bu.

Bu,

Since it appears within the comment, the presence of such character really does NOT make sense right?

[marc weber]

Originally posted by Raghavan Muthu:
... Since it appears within the comment, the presence of such character really does NOT make sense right?

It might make sense. For example...

//Use \u000A for new line

But it won't compile.

[Raghavan Muthu]

Originally posted by marc weber:

It might make sense. For example...

//Use \u000A for new line

But it won't compile.

oh. that's correct. Silly mistake i did!

Thank you Marc.

[Raghavan Muthu]

Hello Marc and Bu,

I found a strange behavior when i am preparing the presentation slides for the fresh buddies.

The same comment containing the line feed character in Unicode form gets compiled when it is present inside the multi-line comment.

Here is the same code but within the multiline comments.

class CommentDoesNotGetCompiled 
{
public static void main(String[] args) 
{
/*
  a comment that doesn't compile '\u000a'
*/
System.out.println("Hello World!");
}
}

The code gets compiled successfully.

But its guaranteed to fail in compilation when its present in the single line comment. I could not find much information about this in JLS as well.(Chapter 3, Lexical Structure).

Any idea about this?

Thanks in advance.

[Jesper de Jong]

Hi Raghavan,

It's not as strange as it looks. \u000a is a newline character. Multi-line comments start with /* and end with */. Newline characters are allowed inside a multi-line comment. These two pieces of code are exactly the same:

/*
  Hello, a \u000a multi-line comment
*/
 
/*
  Hello, a 
 multi-line comment
*/

They are both valid multi-line comments. A single-line comment starts with // and ends with newline. If you use \u000a inside such a comment, the text after the \u000a is put on the next line and is not interpreted as a comment.

// Hello, a \u000a single-line comment
 
// Hello, a 
 single-line comment

You see, the words "single-line comment" are on the next line, not inside the comment anymore, and since it isn't a valid Java statement, you'll get a compiler error.

[Raghavan Muthu]

Yes, that's perfect.

Thank you very much Jesper.

[Peter Mularien]

Actually, this could lead to some interesting trick questions, for example:

    
class UnicodeCommentTrick {
 public static void main(String foo[]) {
  int x=5;
  // do not do this \u000a x=6;
  System.out.println(x);
 }
}

... this will of course print 6!

[Raghavan Muthu]

Yes, thats true as because of its being a single line comment and the character \u000a gets resolved into a newline character thereby making the rest (x=6) gets shifted to the next line as an executable statement.

[Ilakya Mukunth]

I tried to compile the following code and it just compiled fine. but i do not understand the meaning of these constants.
1. char c ='\u0061', c1='\61';
2. System.out.println(c + " " +c1); // a 1

1. float f1 =\u0030;
2. System.out.println(f1); // 0.0

how can we assign unicode constants to float?

[Himai Minh]

A character is actually a 16-bit integer.

char c = '\u0061';
int i1 = c;

You can assign an integer to a character.
You can also assign a float to an integer. The float has 64-bit. A character has 16-bit.A float has enough space to hold a character.

[gurpeet singh]

Himai Minh wrote:A character is actually a 16-bit integer.

char c = '\u0061';
int i1 = c;

You can assign an integer to a character.
You can also assign a float to an integer. The float has 64-bit. A character has 16-bit.A float has enough space to hold a character.

we cannot assign a float to an integer without using casting. secondly a character is a 16-bit signed integer.