How Does Integer.parseInt(String) Work in Java?

What is the internal working mechanism of Integer.parseInt(String) in Java?

String strNum = "123";
int num = Integer.parseInt(strNum); // Converts String to int

The `Integer.parseInt(String)` method in Java is used to convert a string representation of an integer into its numerical form. This method is part of the `Integer` class and is crucial in scenarios where numerical input comes in as strings, such as user input or data from files.

String strNum = "  123  "; // String with leading/trailing spaces
int num = Integer.parseInt(strNum.trim()); // Correctly parses the number after trimming leading/trailing spaces.

Causes

• The method throws a NumberFormatException if the string does not contain a parsable integer.
• Leading or trailing whitespace in the string can cause the method to fail if not handled correctly.

Solutions

• Ensure the string only contains valid numeric characters without any letters or special characters apart from potential leading minus signs.
• Trim white spaces using `strNum.trim()` before parsing, ensuring clean data for conversion.

Mistake: Passing a string with alphabetic characters (e.g., "abc") to Integer.parseInt.

Solution: Use a try-catch block to handle exceptions gracefully.

Mistake: Assuming all numbers will be successfully parsed without validation.

Solution: Always validate the string input or use exception handling to manage potential NumberFormatExceptions.