在Java中使用while循环时出错

Question

I'm a newbie in java from c# background. In c# when i want to make sure the user cannot does null data in the Console Application i make a loop like

static void Main(string[] args)
{
    Console.WriteLine("Enter your name : ");
    string name = Console.ReadLine();

    while (name == "")
    {
        Console.WriteLine("Enter your name : ");
        name = Console.ReadLine();
    }
}

Now I want to implement the same in java. I am using

public static void main(String[] args) {
    // TODO code application logic here
    System.out.println("Enter your name : ");
    String pname;
    Scanner scan=new Scanner(System.in);
    pname=scan.next();

    while ("".equals(pname))
    {
        System.out.println("Enter your name : ");
        pname=scan.next();
    }
}

But when a null value is entered, the output doesn't show the Enter your name again it only moves one line waiting for a value to be entered.

What am i doing wrong?

Answer 1

Try using nextLine() instead. next() only gets up to the next space, nextLine() gets the next linebreak. I vaguely remember this from my java class in college.

Answer 2

   while ("".equals(pname))
        {
           System.out.println("Enter your name : ");
           pname=scan.next();
        }

Instead use

     while (pname.equals(""))
     {
        System.out.println("Enter your name : ");
        pname=scan.next();
     }

If you look at javadocs for equals, you will know what i am talking about. And also a hint, i started using buffred reader when i started coding in java

Answer 3

You can use:

while (pname == null || "".equals(pname))
{
    System.out.println("Enter your name : ");
    pname = scanner.nextLine();
}

Answer 4

I also faced similar type of problem once. The problem is not in while loop. It is in reusing same Scanner object. Try creating new Scanner object each time.

public static void main(String[] args) {
// TODO code application logic here
System.out.println("Enter your name : ");
String pname;
Scanner scan=new Scanner(System.in);
pname=scan.next();

while (pname.equals(""))
{
    System.out.println("Enter your name : ");
    scan = new Scanner(System.in);
    pname=scan.next();
}

}