This is generally done with a simple user-defined function (i.e. Roll-your-own "isNumeric" function).

Something like:

Copypublic static boolean isNumeric(String str) { 
  try {  
    Double.parseDouble(str);  
    return true;
  } catch(NumberFormatException e){  
    return false;  
  }  
}

However, if you're calling this function a lot, and you expect many of the checks to fail due to not being a number then performance of this mechanism will not be great, since you're relying upon exceptions being thrown for each failure, which is a fairly expensive operation.

An alternative approach may be to use a regular expression to check for validity of being a number:

Copypublic static boolean isNumeric(String str) {
  return str.matches("-?\\d+(\\.\\d+)?");  //match a number with optional '-' and decimal.
}

Be careful with the above RegEx mechanism, though, as it will fail if you're using non-Arabic digits (i.e. numerals other than 0 through to 9). This is because the "\d" part of the RegEx will only match [0-9] and effectively isn't internationally numerically aware. (Thanks to OregonGhost for pointing this out!)

Or even another alternative is to use Java's built-in java.text.NumberFormat object to see if, after parsing the string the parser position is at the end of the string. If it is, we can assume the entire string is numeric:

Copypublic static boolean isNumeric(String str) {
  ParsePosition pos = new ParsePosition(0);
  NumberFormat.getInstance().parse(str, pos);
  return str.length() == pos.getIndex();
}

If you'll be processing the number as text, then change:

if (text.contains("[a-zA-Z]+") == false && text.length() > 2){

to:

if (text.matches("[0-9]+") && text.length() > 2) {

Instead of checking that the string doesn't contain alphabetic characters, check to be sure it contains only numerics.

If you actually want to use the numeric value, use Integer.parseInt() or Double.parseDouble() as others have explained below.

As a side note, it's generally considered bad practice to compare boolean values to true or false. Just use if (condition) or if (!condition).

Many options explored at http://www.coderanch.com/t/405258/java/java/String-IsNumeric

One more is

public boolean isNumeric(String s) {  
    return s != null && s.matches("[-+]?\\d*\\.?\\d+");  
}  

Might be overkill but Apache Commons NumberUtils seems to have some helpers as well.