How To Convert a String to Int in Java

In Java, converting a String to an int is a common requirement, especially when working with user input, file parsing, or data received from external sources like APIs. Fortunately, Java provides multiple built-in methods to perform this conversion efficiently and safely.

Below are the most commonly used techniques:

1. Using Integer.parseInt() (Most Common Method)

   This is the recommended and most efficient way to convert a String to an int.

   public class Main {
   	public static void main(String[] args) {
       	String numberString = "123";
       	int number = Integer.parseInt(numberString);
       	System.out.println("Converted int: " + number);
   	}
   }
   

   Pros: Simple, fast, and returns a primitive int.

   Note: Throws NumberFormatException if the string is not a valid integer.

2. Using Integer.valueOf() (Returns Integer Object)

   This method converts the String to an Integer (object), which can be unboxed to int.

   public class Main {
   	public static void main(String[] args) {
       	String numberString = "456";
       	int number = Integer.valueOf(numberString);
       	System.out.println("Converted int: " + number);
   	}
   }
   

   Pros: Useful when you specifically need an Integer object.

   Note: Also throws NumberFormatException for invalid input.

3. Using parseInt() with a Specific Radix

   You can also specify a radix (base) while parsing the string. This is especially helpful when dealing with binary, hexadecimal, or octal numbers.

   public class Main {
   	public static void main(String[] args) {
       	String binaryString = "1010";
       	int number = Integer.parseInt(binaryString, 2); // Binary to Decimal
       	System.out.println("Binary to int: " + number);
   	}
   }
   

   Pros: Converts numbers in various numeral systems to int.

   Note: Parsing binary (2), octal (8), decimal (10), or hexadecimal (16) strings.

Exception Handling Tip

All the above methods can throw a NumberFormatException if the input string is not a valid number. Wrapping the parsing code in a try-catch block is a good practice to handle such scenarios gracefully.

try {
    int number = Integer.parseInt("abc"); // Will throw exception
} catch (NumberFormatException e) {
    System.out.println("Invalid number format!");
}

Final Thoughts

Choosing the right method depends on your use case. If you just need a primitive int, go with Integer.parseInt(). If you require an Integer object (e.g., for collections like List<Integer>), use Integer.valueOf(). When dealing with numbers in different bases, the radix-aware version of parseInt() is your go-to tool.

Always remember to validate or handle exceptions when working with external or user-provided data to avoid runtime errors.