Verify if a String is numeric

[Rafael Afonso]

Hello:
I find that this is a pparently silly doubt (so I am writing in beginner's forum): I never found a method in the API of the Java to verify if a String is numerical or not, either Integer or floating-point. A way - that I don't like - would be to make something thus:

  
public boolean isInt(String str) { 
   boolean isInteger = true; 
   try { 
     int i = Integer.parseInt(str); 
   } catch(NumberFormatException nfe) { 
      isInteger = false; 
   } 
   return isInteger; 
} 

Other way - that does not use exception - would be thus:

public boolean isInt(String str) { 
   boolean isInteger = true; 
   int size = str.length(); 
   for(int i = 0; (i < size) && isInteger; i ++) { 
      // to individual caracters, Java has a method to avaliate
      isInteger = Character.isDigit(str.charAt(i)); 
   } 
   return isInteger; 
} 

In that if it relates to the floating-point numbers (float and double), still we must take in consideration the point decimal, that varies of locale for locale ("," in Brazil, "." in U.S.A., for example).
At last, is there only these alternatives above, that we must construct "manually"? Somebody has some idea?
Thanks,

[Adrian Airloy]

Hey Rafael
If I was checking if a String was an int or not, I would tend to use the 'valueOf' method in the Integer class. And extract the appropriate int value from it or throw an exception.
However if you are only intrested in checking if a String is an int or not (as a boolean response), then what you have written above appears to be right.
[ March 08, 2003: Message edited by: Adrian Miranda ]

[Rafael Afonso]

Adrian:
From your suggestion, the first code would be thus:

public boolean isInt(String str) {    
   boolean isInteger = true;    
   try {      
      Integer i = Integer.valueOf(str);    
   } catch(NumberFormatException nfe) {
      isInteger = false;    
   }    
   return isInteger; 
} 

It does not make difference to final goal. But thanks anyway.

[John Smith]

In that if it relates to the floating-point numbers (float and double), still we must take in consideration the point decimal, that varies of locale for locale ("," in Brazil, "." in U.S.A., for example).
At last, is there only these alternatives above, that we must construct "manually"? Somebody has some idea?

I think what you looking for is this:

    NumberFormat localFormat = NumberFormat.getInstance(Locale.ITALY);
    String numberString = "123.456,789"; // European (and Brasilian?) format
    ParsePosition parsePosition = new ParsePosition(0);
    double number = localFormat.parse( numberString, parsePosition).doubleValue();
    System.out.println( " number = " + number );

Eugene.