Scanner class problems

[sypherz]

hi, i want to read in entire lines of from the user
and have the loop terminate when user hits enter on a blank line

the loop never ends! please help. my this is just a test class for
the rest of a program i am just abo0ut finished

this is what i have for the loop:

Code:

String aString;
		System.out.println("Enter sentences, after each sentence hit enter\n" + 
						   "hit enter on an empty line to stop :\n");
		do
		{
			System.out.println("beginning of iteration\n");
			aString = sc.nextLine();
			stringData.add(aString);
			System.out.println("end of iteration\n");
		}while(sc.nextLine() != null);

[sukatoa]

null means, nothing... 0

How about enter? that generates a newline right?values 0A in hex....

Try to print what

Code:

while(sc.nextLine() != null);

prints, since that comparison always true, then sc.nextLine() should have captured some text from console...

and i guess, that will prints "end of iteration"

try like,

Code:

while(sc.nextLine().equals("");

or another flag that could negate the comparison,

eg. if(sc.nextLine().equals("x") then terminate....

[sypherz]

yes! thank you. i though that null == " " for some reason.

[Eranga]

You got a collision with null and empty string there.

[sypherz]

String aString = null;//never creates sring object

String aString = " ";//memory IS allocated for string object.

i guess thats the difference right?

[pjm35@st-and.ac.uk]

Yeah, the null is just a null pointer, i.e. a pointer which doesn't point to any object in memory. With the second one the string " " is stored in memory and the String object aString contains a pointer to that string.

When you test the user input first use the trim() method on the string. That is:

Code:

while(sc.nextLine().trim()!="");

[Eranga]

You can still test null too here. It's better too.