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Thread: checking for empty strings?

  1. #1
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    Default checking for empty strings?

    I'm trying to check for empty strings with a Scanner and I'm not sure how to loop it so that it asks for the correct input.

    So I want to use
    System.out.print("Enter your First Name: ");
    String employeeFirstName = j.next(); //first name declared
    System.out.print("Enter your Last Name: ");
    String employeeLastName = j.next(); //last name declared

    and I want to have it check so if the user enters a number or a blank that it asks for the input again. I tried using both if and while loops and it would still print "enter last name" after the first name and then also say it was invalid and crash the program.


  2. #2
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    Default Re: checking for empty strings?

    You need to use try, catch blocks for this.
     public static void main(String[] args) throws InputMismatchException
          {    boolean flag = true;
               int i;
               Scanner j = new Scanner(System.in);
               String employeeFirstName = null;
          do{   
        	  try
              {        	     
     
                System.out.print("Enter your First Name: ");
                employeeFirstName = j.next(); //first name declared
                for(i=0;i<employeeFirstName.length();i++)
                   	if(!((employeeFirstName.charAt(i)>= (int) 'A') && (employeeFirstName.charAt(i)<= (int)'z')))
                		throw new InputMismatchException();
     
     
                flag=!flag;
              }
     
              catch(InputMismatchException e)
              {
            	  System.out.println("Invalid input.Try again");
              }
             }while(flag);
     
          do{   
        	  try
              {        	     
        		  System.out.print("Enter your Last Name: ");
        		  String employeeLastName = j.next(); //last name declared
        		    for(i=0;i<employeeLastName.length();i++)
        		      	if(!(employeeLastName.charAt(i)>= (int) 'A') || !(employeeLastName.charAt(i)<= (int)'z'))
        		    		throw new InputMismatchException();
                       System.out.println("Your name is: "+employeeFirstName+" "+employeeLastName);
                   flag=!flag;
              }
     
              catch(InputMismatchException e)
              {
            	  System.out.println("Invalid input.Try again");
              }
             }while(!flag);
          }
    Last edited by helloworld922; October 31st, 2010 at 09:49 PM.

  3. #3
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    Default Re: checking for empty strings?

    That is probably proper, but shouldn't this work also...since you are using a boolean in yours anyway, why use the catch blocks?

    boolean goodInput = false;

    while(!goodInput) {
    	goodInput = true;
            System.out.print("Enter first name: ");
    	employeeFirstName = j.next();
    //Nice for loop to ensure all chars are letters
    	for(i=0;i<employeeFirstName.length();i++) {
                    if(!((employeeFirstName.charAt(i)>= (int) 'A') && (employeeFirstName.charAt(i)<= (int)'z'))) {
    		    goodInput = false;
    		    System.out.println("Bad input, try again.");
                        continue;
                    }
    	}
    }
    And then another for last name, resetting goodInput to false of course.

  4. #4
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    Default Re: checking for empty strings?

    This is a better code than mine. But mine would work too. Thanks for showing an aliter.

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