Converting a String to an Integer is a common operation in Java, especially when dealing with user input or reading data from files. In this blog post, we will explore various methods to convert a String to an Integer and provide practical examples with outputs to illustrate each approach.

Method 1: Using Integer.parseInt() Method

The Integer.parseInt() method is a straightforward way to convert a String to an Integer. It parses the string argument as a signed decimal integer and returns the resulting numeric value.

Example:

public class StringToIntegerExample {
    public static void main(String[] args) {
        String strNumber = "42";

        try {
            // Convert String to Integer using parseInt()
            int intValue = Integer.parseInt(strNumber);
            System.out.println("Input String: " + strNumber);
            System.out.println("Integer Value: " + intValue);
        } catch (NumberFormatException e) {
            System.out.println("Error: Invalid input for integer conversion");
        }
    }
}

Output:

Input String: 42
Integer Value: 42

Method 2: Using Integer.valueOf() Method

The Integer.valueOf() method converts a String to an Integer object. It returns an Integer instance representing the specified int value if the String is a valid representation of an integer.

Example:

public class StringToIntegerExample {
    public static void main(String[] args) {
        String strNumber = "100";

        try {
            // Convert String to Integer using valueOf()
            Integer integerValue = Integer.valueOf(strNumber);
            System.out.println("Input String: " + strNumber);
            System.out.println("Integer Value: " + integerValue);
        } catch (NumberFormatException e) {
            System.out.println("Error: Invalid input for integer conversion");
        }
    }
}

Output:

Input String: 100
Integer Value: 100

Method 3: Using NumberFormat.parse() Method

You can also use NumberFormat to parse the String and convert it to an Integer.

Example:

import java.text.NumberFormat;
import java.text.ParseException;

public class StringToIntegerExample {
    public static void main(String[] args) {
        String strNumber = "2022";

        // Convert String to Integer using NumberFormat
        try {
            NumberFormat numberFormat = NumberFormat.getInstance();
            int intValue = numberFormat.parse(strNumber).intValue();
            System.out.println("Input String: " + strNumber);
            System.out.println("Integer Value: " + intValue);
        } catch (ParseException e) {
            System.out.println("Error: Invalid input for integer conversion");
        }
    }
}

Output:

Input String: 2022
Integer Value: 2022

Method 4: Using Scanner class

The Scanner class can also be used to convert a String to an Integer.

Example:

import java.util.Scanner;

public class StringToIntegerExample {
    public static void main(String[] args) {
        String strNumber = "999";

        // Convert String to Integer using Scanner
        try {
            Scanner scanner = new Scanner(strNumber);
            int intValue = scanner.nextInt();
            System.out.println("Input String: " + strNumber);
            System.out.println("Integer Value: " + intValue);
        } catch (NumberFormatException e) {
            System.out.println("Error: Invalid input for integer conversion");
        }
    }
}

Output:

Input String: 999
Integer Value: 999

Conclusion

Converting a String to an Integer is a fundamental operation in Java. You can use methods like Integer.parseInt(), Integer.valueOf(), NumberFormat or Scanner to achieve this. In this blog post, we provided practical examples with outputs to demonstrate each method's effectiveness. Remember to handle exceptions appropriately to gracefully handle invalid input and ensure the reliability of your code.