如何验证Java中的数字输入？

Question

I've validated that the entered string is a number.

while (true) {

    try {
        numberOfmiles = Double.parseDouble(JOptionPane.showInputDialog(null," Enter Positive Number"));       
         break;
    }

    catch (NumberFormatException nfs) {
         JOptionPane.showMessageDialog(null, "Please Enter a Positive number");
    }
}

I need to also check that it is a positive number. How would I do that?

Answer 1

Try:

double numberOfMiles;
do{
  try{
    numberOfmiles = Double.parseDouble(JOptionPane.showInputDialog(null," Enter Positive Number"));       
  }catch(NumberFormatException nfe){
    JOptionPane.showMessageDialog(null, "Please Enter a Positive number");
    numberOfMiles = -1;
  }
}while(numberOfMiles < 0);

Answer 2

if (numberOfmiles <0)
    JOptionPane.showMessageDialog(null, "Warning, enter positive numbers only");

Answer 3

I assume you have a textfield used as input try this:

 private void jTextField1KeyTyped(java.awt.event.KeyEvent evt) {                                     
        char c = evt.getKeyChar();
        if ( ((c<'0')||(c>'9'))&& (c != KeyEvent.VK_BACKSPACE))
        {
        JOptionPane.showMessageDialog(null, "Just positive numbers are allowed");                        
        }
else
{
  //non action until a button is pressed
}

:)

Answer 4

        while(true){
      String userInput=JOptionPane.showInputDialog(null," Enter Positive Number");
        if(userInput.matches("^\\d+(.\\d+)?$")){
         double numberOfmiles=Double.parseDouble(userInput);
         if (numberOfmiles <0){
        JOptionPane.showMessageDialog(null, "Warning, enter positive numbers only")
        }
        else{
        //successful input
        break;
        }
    }
        else{
            JOptionPane.showMessageDialog(null, "Just positive numbers are allowed"); 
        }

   }