Check If a String Is a Valid Number in Java

In Java, verifying whether a string is a valid number is a common requirement in various applications. This process ensures that the string can be safely converted to a numerical type without causing runtime exceptions. To validate if a string can be converted to these types, we use the Integer.parseInt() and Float.parseFloat() methods, respectively.

Problem Statement

Given a string that may contain an integer or a float value, write a Java program to check whether it is valid number or not.

Input

    "100" //string value

Output

    100 // integer value

Check if a string is a valid number for integer values

To check if a string is a valid Integer, use the Integer.parseInt() method, with the string to be checked passed as a parameter.

• Step 1: Use Integer.parseInt() to try converting the string to an integer.
• Step 2: If it throws NumberFormatException, the string is not a valid integer.

Example

public class Demo {
    public static void main(String args[]) throws Exception {
        String id = "100";
        int val = Integer.parseInt(id);
        System.out.println(val);
    }
}

Output

100

Check if a string is a valid number for float values

To check if a string is a valid Float, use the Float.parseFloat() method, with the string to be checked passed as a parameter.

• Step 1: Use Float.parseFloat() to try converting the string to a float.
• Step 2: If it throws `NumberFormatException`, the string is not a valid float.

Example

The following is an example that checks for valid float −

public class Demo {
    String id = "100.5";
    float val = Float.parseFloat(id);
    System.out.println(val);
    }
}

Output

100.5

Conclusion

We can conclude that by using Integer.parseInt() and Float.parseFloat(), along with exception handling, you can effectively check if a string is a valid number in Java.