Thread: system.out prints twice in a small program

hi friends

i am new to java and started a week back

even in a simple program shown below

system.out prints twice i am using netbeans ide

it prints as bellows

press a key : a
press a key : press a key :

public class DoWhile {
 
    /**
     * @param args the command line arguments
     * @throws java.io.IOException
     */
    public static void main(String[] args)
            throws java.io.IOException
    {
        char ch;
        do {
        System.out.print("press a key : ");
        ch = (char) System.in.read();
        }
        while(ch != 'q');
        }
 
}

kindly help

You have a do while, so it's going to print out at least once. It prints out, then it reads in a single byte, which is a. Notice how after you pushed a, you also pressed enter (the newline character), so that's still "in" System.in.

It checks whether a is equal to q, and since it's not, it goes through again. It prints out the message, and then reads in the newline character you left in there. It then checks whether the newline character is equal to q, and since it's not, it goes through yet again.

You should probably be using the Scanner class.

Originally Posted by vinaysagar

as i am totally new i am doing it as said in the book and dont know how to use scanner

Don't be afraid to google your problem. This is the second result for googling "Java Scanner": Scanning (The Java™ Tutorials > Essential Classes > Basic I/O)