How to convert a String to an int in Java? (Step-by-Step Guide)
Use Integer.parseInt() for direct string-to-int conversion, which throws NumberFormatException for invalid inputs like "12.3" or "abc"; wrap in try-catch for untrusted input. Integer.valueOf() returns an Integer object and behaves identically but is preferred for collections. Always trim whitespace and validate null/empty strings; avoid deprecated new Integer(String) and naive digit checks.
Use Integer.parseInt() for simple, direct conversion — it throws NumberFormatException if the string isn’t a valid integer.
Using Integer.parseInt() (most common)
This method converts a string containing only digits (optionally with a leading or -) into a primitive int.
- Works with strings like
"123","-456"," 789" - Fails on
"12.3","abc","", or"123abc"— throwsNumberFormatException - Always wrap in a
try-catchif the string source is untrusted
Using Integer.valueOf() (returns Integer object)
This returns an Integer wrapper object instead of a primitive int. It internally calls parseInt(), so behavior and exceptions are identical.
- Use when you need an
Integer(e.g., for collections likeArrayList<integer></integer>) - Autoboxing usually makes
int x = Integer.valueOf("42");work seamlessly - Slightly more overhead than
parseInt(), but negligible in most cases
Handling invalid input safely
Instead of letting your app crash, validate or recover gracefully:
- Check for
nullor empty strings before parsing - Catch
NumberFormatExceptionand provide fallback logic (e.g., default value or error message) - For user input, consider using a utility method that returns
Optional<integer></integer>or a default int
What NOT to do
Avoid unsafe shortcuts:
- Don’t use
new Integer(String)— it’s deprecated since Java 9 - Don’t rely on
Character.isDigit()alone — it won’t handle signs or multi-digit logic correctly - Don’t assume trimming whitespace isn’t needed —
" 123 "will fail unless trimmed first
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