---
title: NumberFormatException in Java- Scaler Topics
description: Learn about NumberFormatException in detail on Scaler Topics with all examples and all the programs involved in it; read to know more.
category: Java
author: Mansi
---
:::section{.abstract}

`NumberFormatException` in Java is an unchecked exception, a subclass of `IllegalArgumentException`. This class implements a serializable interface. It occurs while converting a String with an improper format to other numeric forms like Integer or float.

A `parseInt()` method converts a string to an integer type when operating with the string. parseInt() method can be used in two ways, as given below:

// This function parses the string argument as a signed decimal integer
public static int parseInt(String s) throws NumberFormatException
 
//This function parses the string argument as a signed integer in the radix specified

public static int parseInt(String s, int radix) throws NumberFormatException
 

Both methods convert a string to an integer. The only difference between these **`two syntaxes`** is the parameter radix. When **`radix=10`**, the first method is considered equivalent to the second method.
:::
:::section{.main}
## Constructors of NumberFormatException

| Constructor | Description |
| :--------: | :--------: |
| public NumberFormatException() | default constructor, an exception, NumberFormatException with no description. |
|public NumberFormatException(String msg)|Constructs an exception, NumberFormatException, with a detailed description of it, parameterized, with an error message .|
:::
:::section{.main}
## Common Reasons for NumberFormatException
There are various problems related to improper string formatting. Here are a few important reasons for NumberFormatException in java:
* **Null input string:**

Integer.parseInt("null");

* **Input string which is empty:**

Float.parseFloat(“”);

* **Leading or trailing white spaces in input string:**

Integer abc=new Integer(“  123 “);

* **Extra symbol in input string:**

Float.parseFloat(4,123);

* **Input string with data which is non-numeric:**

Double.parseDouble(“FifityFive”);

* **Alphanumeric input string:**

Integer.valueOf(“33.three”);

* **Input string with exceeded range of datatype:**

Integer.parseInt(“1826589745243”);

* **Type mismatch between the value of the input string and its method:**

Integer.parseInt("12.33");

:::
:::section{.main}
## Example of NumberFormatException

Program to illustrate **`NumberFormatException`** in java.
In this example, we will try to understand how and why NumberFormartException occurs.

import java.util.Scanner;
public class Test {
 
	// Main method
	public static void main(String[] arg)
	{
		// variable for holding the input
		int number;
 
		// scanner class for taking input from the user
		Scanner sc = new Scanner(System.in);
 
		//If the condition is true, it means run the loop until the integer is valid
		while (true) {
			System.out.println("Enter an Integer: ");
 
			// Try block to catch the exception
			try {
 
				// Parsing the input of user
				number = Integer.parseInt(sc.next());
				// prints if the number is valid
				System.out.println("You entered: "
								+ number);
 
				// out of loop
				break;
			}
 
			// Catch block for handling NumberFormatException in java
			catch (NumberFormatException e) {
				System.out.println(
					"NumberFormatException occurred");
			}
		}
	}
}

**Output**:

Enter an Integer: 15
You entered: 15

Enter an Integer: 13.3
NumberFormatException occurred
Enter any valid Integer: 
13.2
NumberFormatException occurred
Enter an Integer: 
15
You entered: 15

**Explanation**: As per the code, as soon as the user enters a number other than an Integer, like **`double or float`**, the NumberFormatException occurs.

**Flow of the given code:**

* Input is taken from `user`
* The input is parsed using `parseInt`
* If there is an `error` while parsing
* `NumberFormatException` is thrown
* Else `Output` is printed
:::
:::section{.main}
## How to Handle NumberFormatException?
The NumberFormatException in java can be handled in **`two`** ways:
1. Using the **`block try-catch** : This involves surrounding the code that might cause the exception with a try block and handling the exception in a catch block.
For example:

class Main {
   public static void main(String args[]) {
      try {
         // parse the string "12a" to an integer
         int number = Integer.parseInt("12a");
         System.out.println("Number: " + number);
      } catch (NumberFormatException e) {
         // catch the exception if the string is not a valid integer
         System.out.println("Wrong data format: " + e.getMessage());
      }
   }
}

**Output**:

Wrong data format: For input string: "12a"

2. Using the `throws` keyword: This involves declaring that a method might throw a specific exception and leaving it to the calling method to handle it. For example, a method parsing a string to an integer might declare that it throws a `NumberFormatException` if the string is not valid. The calling method would then have to handle this exception using a `try-catch` block or declare that it throws the exception using the `throws` keyword.

For example:

class Main {
   public static int parseInt(String str) throws NumberFormatException {
      return Integer.parseInt(str);
   }
   public static void main(String args[]) {
      try {
         //Call the parseInt method and pass the string "12a" as argument
         int number = parseInt("12a");
         System.out.println("Number: " + number);
      } catch (NumberFormatException e) {
         // catch the exception if the string is not a valid integer
         System.out.println("Wrong data format: " + e.getMessage());
      }
   }
}

**Output**:

Wrong data format: For input string: "12a"

:::
:::section{.summary}
## Conclusion
* `NumberFormatException` in java is thrown while converting an improperly formatted string to a numeric value like an integer or float.
* It is an unchecked exception known as a run-time exception. The `try-catch block` handles this exception.
* Constructors of NumberFormatException:
* public NumberFormatException()
* public NumberFormatException(String msg)
* The NumberFormatException in java can be handled by using a try-catch block or using the throws keyword

:::