How to Convert a String to a Number in Java?

What are the ways to convert a String to a numeric type in Java?

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

Converting a string to a number in Java is a common operation that can be achieved using several methods. The most straightforward methods include using wrapper classes like `Integer`, `Double`, and `Float`. These classes provide static methods to parse strings and convert them to corresponding numeric types.

// Example of String to int conversion
String numericString = "456";
int number = Integer.parseInt(numericString);

// Example of String to double conversion
String doubleString = "456.78";
double doubleValue = Double.parseDouble(doubleString);

// Handling NumberFormatException
try {
    int invalidNumber = Integer.parseInt("123abc");
} catch (NumberFormatException e) {
    System.out.println("Invalid format: " + e.getMessage());
}

Causes

• Incorrect formatting of the string: Ensure the string is numeric without spaces or special characters.
• Using the wrong method for conversion: Different methods exist for integers, floating-point numbers, etc.
• Locale issues: If the string contains commas or other locale-specific markers that interfere with parsing.

Solutions

• Use `Integer.parseInt(String)` for converting to an int.
• Use `Double.parseDouble(String)` for converting to a double.
• Use `Float.parseFloat(String)` for converting to a float.
• Handle exceptions properly using try-catch blocks to avoid runtime errors.
• Consider using `NumberFormat` for more complex number parsing, especially when dealing with locales.

Mistake: Forgetting to handle the NumberFormatException when parsing.

Solution: Always wrap parsing in a try-catch block to catch and handle exceptions.

Mistake: Using `int` instead of `Integer` for null check.

Solution: Choose `Integer` to avoid NullPointerExceptions when the string may be null.

Mistake: Using incorrect methods for conversion, e.g., using `Integer.parseDouble()` instead of `Double.parseDouble()`.

Solution: Always use the correct parsing method corresponding to the target numeric type.