Sometimes we need to check whether the user input is a valid number or not. If not, we need to tell the user to input a valid number again. In this example, we will show you two methods about how to verify a valid numeric value in a Java String variable.
1. Use Double.parseDouble() and Integer.parseInt().
/* Use Double and Integer parse method to check. */
private static boolean ifValidNumber(String str)
{
boolean ret = true;
try
{
if(str!=null)
{
str = str.trim();
int dotIndex = str.indexOf(".");
/* If contain dot, then it should be a double number.*/
if(dotIndex>-1)
{
Double.parseDouble(str);
}else
{
/*If not contain dot, then it should be a integer String. */
Integer.parseInt(str);
}
}
}catch(NumberFormatException ex)
{
/* If parse String method throw a NumberFormatException, then it is not a String. */
ex.printStackTrace();
ret = false;
}
return ret;
}
2. Use Apache Commons Lang StringUtils.
- Go to Apache Commons Lang Project Home Page.
- Click the Download link in the left panel.
- Download the latest stable version of Apache Commons Lang on the download page.
- Extract the download zip file into a local folder, such as C:/WorkSpace/dev2qa.com/Lib.
- Add the commons-lang3-3.6.jar file into your java project’s build path. Right-click the java project, click ” Build Path —> Configure Build Path “.
- Click the ” Add External JARS ” button in the popup dialog.
- Browse to the extracted zip file folder, select commons-lang3-3.6.jar. Click OK to add it.
- Now you can use the below java code to implement this function.
/* Use Apache Commons Lang project StringUtils to check. */ private static boolean ifValidNumberByApacheCommonsLang(String strNum) { boolean ret = StringUtils.isNumeric(strNum); return ret; }
3. Java Main Method.
public static void main(String[] args) {
String strArr[] = {"123", "12.3", "123df56", "abcde", "[email protected]"};
for(String strNum : strArr)
{
//boolean isValidNumber = CheckValidNumberInJavaString.ifValidNumber(strNum);
boolean isValidNumber = CheckValidNumberInJavaString.ifValidNumberByApacheCommonsLang(strNum);
if(isValidNumber)
{
System.out.println(strNum + " is a valid number");
}else
{
System.out.println(strNum + " is not a valid number");
}
}
}
