string to float

[Sungron]

Hi, how can I convert java String to float?
I tried

   float f = Float.valueOf(str).floatValue();

but It gave me exception "NumberFormatException"...
thanks for any help guys..

[JosAH]

Hi, how can I convert java String to float?
I tried

   float f = Float.valueOf(str).floatValue();

but It gave me exception "NumberFormatException"...
thanks for any help guys..

That method works (also have a look at the parseFloat( ... ) method) but your String str didn't contain a valid floating point number representation.

kind regards,

Jos

[Sungron]

Oh, damn how silly is me....now I see, just too much C, I expected it to return 0...
hmm so how can I verify is string really a float? Such exceptions are annoying since they seem to stop whole function...

[Turtle]

Exceptions don't need to stop a function ("method" in java terminology).
Most exceptions can be recovered from.
Infact, they let you write cleaner code because you aren't inserting little checks and thus the purpose of a code block is clearer. Instead you can wrap problem code in a "try catch" block and handle the exceptions at the end.

I have included a code sniplet the demonstrates forcing the user to input a valid float. If the float is invalid, the user is hassled until they do enter a correct value.

import java.io.Console;

class TestFloat {
	
	public static void main(String[] args) {
		
		// Get console object to read from console...
		Console cons;
		if ((cons = System.console()) == null){
			System.out.println("Can't access console, closing program");
			System.exit(1);
		}
		
		// Prompt user for a valid float, repeat until a valid float is entered
		String line;
		float f;
		while(true) {
			// Prompt user for float
			System.out.print("Please enter a valid float: ");
			// Read in user input as string
			line = cons.readLine();
			
			// Wrap conversion code in a try catch block to handle the exception
			try {
				// Try convert String to float (may throw exception)
				f = Float.valueOf(line);
				// Exit while loop if an exception is not thrown
				break;
			} catch(NumberFormatException e) {
				// An exception was thrown, inform user and repeat loop
				System.out.println("That is not a valid float");
			}
		}
		
		// A valid float value was (eventually entered), display it
		System.out.println("Float value was: " + f);
		
	}
}

Check out: Lesson: Exceptions (The Java™ Tutorials > Essential Classes) for details on exceptions.

Hope this helps :-)