How to Convert String to int in Java

Introduction

Converting a String to an int in Java is a common task that can be useful in various scenarios, such as parsing user input, reading data from files, or handling configuration parameters. In Java, this conversion can be done using several methods. This blog post will explore different methods to convert a String to an int in Java.

Table of Contents

1. Using Integer.parseInt()
2. Using Integer.valueOf()
3. Handling NumberFormatException
4. Complete Example Program
5. Conclusion

1. Using Integer.parseInt()

The Integer.parseInt() method parses the string argument as a signed decimal integer.

Example:

public class StringToIntUsingParseInt {
    public static void main(String[] args) {
        String strValue = "12345";

        // Convert string to int using Integer.parseInt()
        int intValue = Integer.parseInt(strValue);

        System.out.println("String value: " + strValue);
        System.out.println("Int value: " + intValue);
    }
}

Output:

String value: 12345
Int value: 12345

Explanation:

• Integer.parseInt(strValue) converts the string value to its int representation.

2. Using Integer.valueOf()

The Integer.valueOf() method returns an Integer instance representing the specified string value. This method can also be used to convert a String to an int.

Example:

public class StringToIntUsingValueOf {
    public static void main(String[] args) {
        String strValue = "54321";

        // Convert string to int using Integer.valueOf()
        int intValue = Integer.valueOf(strValue);

        System.out.println("String value: " + strValue);
        System.out.println("Int value: " + intValue);
    }
}

Output:

String value: 54321
Int value: 54321

Explanation:

• Integer.valueOf(strValue) converts the string value to its int representation.

3. Handling NumberFormatException

Both Integer.parseInt() and Integer.valueOf() throw a NumberFormatException if the string cannot be parsed as an integer. It is essential to handle this exception to ensure the robustness of your code.

Example:

public class StringToIntHandlingException {
    public static void main(String[] args) {
        String strValue = "12345a"; // Invalid integer string

        try {
            // Attempt to convert string to int using Integer.parseInt()
            int intValue = Integer.parseInt(strValue);
            System.out.println("String value: " + strValue);
            System.out.println("Int value: " + intValue);
        } catch (NumberFormatException e) {
            System.out.println("Invalid string format for parsing as int: " + strValue);
        }
    }
}

Output:

Invalid string format for parsing as int: 12345a

Explanation:

• A try-catch block is used to handle the NumberFormatException that occurs when the string cannot be parsed as an integer.

4. Complete Example Program

Here is a complete program that demonstrates all the methods discussed above to convert a String to an int in Java.

Example Code:

public class StringToIntExample {
    public static void main(String[] args) {
        String strValue1 = "12345";
        String strValue2 = "54321";
        String strValue3 = "12345a"; // Invalid integer string

        // Using Integer.parseInt() Method
        try {
            int intValue1 = Integer.parseInt(strValue1);
            System.out.println("Using Integer.parseInt():");
            System.out.println("String value: " + strValue1 + " -> Int value: " + intValue1);
        } catch (NumberFormatException e) {
            System.out.println("Invalid string format for parsing as int: " + strValue1);
        }

        // Using Integer.valueOf() Method
        try {
            int intValue2 = Integer.valueOf(strValue2);
            System.out.println("\nUsing Integer.valueOf():");
            System.out.println("String value: " + strValue2 + " -> Int value: " + intValue2);
        } catch (NumberFormatException e) {
            System.out.println("Invalid string format for parsing as int: " + strValue2);
        }

        // Handling NumberFormatException
        try {
            int intValue3 = Integer.parseInt(strValue3);
            System.out.println("\nHandling NumberFormatException:");
            System.out.println("String value: " + strValue3 + " -> Int value: " + intValue3);
        } catch (NumberFormatException e) {
            System.out.println("Invalid string format for parsing as int: " + strValue3);
        }
    }
}

Output:

Using Integer.parseInt():
String value: 12345 -> Int value: 12345

Using Integer.valueOf():
String value: 54321 -> Int value: 54321

Handling NumberFormatException:
Invalid string format for parsing as int: 12345a

5. Conclusion

Converting a String to an int in Java can be accomplished in several ways. The Integer.parseInt() and Integer.valueOf() methods are both straightforward and widely used. It is essential to handle the NumberFormatException to ensure your code is robust and can handle invalid input gracefully. By understanding these different methods, you can choose the one that best fits your needs and coding style.

Happy coding!