Ending While loop with blank line(Enter key) inside SwitchCase

Question

*amended input scan
I'm trying to end a while loop with enter key/blank line Test codes below works fine.

    Scanner scan = new Scanner(System.in);
    String line;

    while ( (line=scan.nextLine()).length() > 0)  
    {
        System.out.println(line);
    }

However, when I integrate it within my main program(while loop placed within int switch case within a do-while loop) the program skips the codes @case2 and will continue do-while loop

int input;
do{
      System.out.print("Choose a function (-1 to exit): ");
      input=scan.nextInt();
      switch (input)
      {
          case 1:
          break;
          case 2:
          //same while loop here
          break;
      }

  }while(input!=-1);

Sample output:

Choose a function (-1 to exit): 1
Choose a function (-1 to exit): 2
//skip case2 coding
Choose a function (-1 to exit): 1
Choose a function (-1 to exit): -1
//program ends

Answer 1

I'm not 100% sure, but I think that scanner is not reading all input. There's a blank line (a newline character) in the buffer when the Scanner starts to read, so it returns an empty line, which causes your line length to be 0 and exit the loop immediately.

Here's my best guess as to what your current program is:

public class InputTest
{

   public static void main( String[] args )
   {
      Scanner scan = new Scanner( System.in );
      int input = 0;
      do {
         System.out.print( "Choose a function (-1 to exit): " );
         input = scan.nextInt();
         switch( input ) {
            case 1:
               System.out.println("..1");
               break;
            case 2:
               System.out.println("..2");
               //same while loop here
               String line = scan.nextLine();
               System.out.println(">>"+line+"<<");
               while( line.length() > 0 ) {
                  System.out.println( "  Read line: " + line );
                  line = scan.nextLine();
                  System.out.println(">>"+line+"<<");
               }
               break;
         }
      } while( input != -1 );
   }
}

And its output:

run:
Choose a function (-1 to exit): 1
..1
Choose a function (-1 to exit): 2
..2
>><<
Choose a function (-1 to exit): -1
BUILD SUCCESSFUL (total time: 11 seconds)

You can see that the line prints as >><< which means it was read but empty. I think the left over newline from '2' above, since a newline isn't part of the number 2 and would be left in the buffer.

Answer 2

Thanks for the help! After some trial and error, I got the code to work

Scanner scan = new Scanner(System.in);
  int input;
  do{
  System.out.print("Choose a function (-1 to exit): ");
  input=scan.nextInt();       

  switch (input)
  {
  case 1:
     break;
  case 2:
     System.out.println("..2"); 
     String line;
     scan.nextLine();//skips the entire current line.
     while ( (line=scan.nextLine()).length() > 0)  
        {
        System.out.println(line);
        }
        break;
     }
  }while(input!=-1);    

The System.out.println() seems to clear interference from scan.nextInt(),
The just my theory though

Answer 3

Scanner is not able to read any input as there is no tokens (after you press 2) in current line .

You need to use scan.nextLine() (to ignore the rest of the currrent line and move the scanner to beginning of next line) before reading the input.

do{

      System.out.print("Choose a function (-1 to exit): ");
      input=scan.nextInt();       

      switch (input)
      {
      case 1:
         break;
      case 2:
         scan.nextLine();//skips the entire current line.
         while ( (line=scan.nextLine()).length() > 0)  
            {
            System.out.println(line);
            }
            //System.out.println(line.length());
            break;
         }
}while(input!=-1);

Output

Choose a function (-1 to exit): 2
hello
hello
bye
bye

Choose a function (-1 to exit):-1

Hope it helps you.