java.lang.IllegalArgumentException: Invalid argument
java.lang.IllegalArgumentException: timeout value is negativeA method was called with an argument that’s not valid — wrong range, null when not allowed, or wrong format.
Fix 1: Validate Input Before Passing
// ❌ Passing negative value
Thread.sleep(-1000); // 💥 IllegalArgumentException
// ✅ Validate first
if (timeout > 0) {
Thread.sleep(timeout);
}Fix 2: Null Argument
// ❌ Passing null to a method that doesn't accept it
Path path = Paths.get(null); // 💥
// ✅ Check for null
if (filename != null) {
Path path = Paths.get(filename);
}Fix 3: Enum.valueOf with Invalid Name
// ❌ String doesn't match any enum constant
Color c = Color.valueOf("PURPLE"); // 💥 If PURPLE doesn't exist
// ✅ Handle gracefully
try {
Color c = Color.valueOf(input.toUpperCase());
} catch (IllegalArgumentException e) {
Color c = Color.RED; // Default
}Fix 4: Date/Time Parsing
// ❌ Invalid date format
LocalDate.parse("2026-13-01"); // 💥 Month 13 doesn't exist
// ✅ Validate or catch
try {
LocalDate date = LocalDate.parse(input);
} catch (DateTimeParseException e) {
System.out.println("Invalid date: " + input);
}Fix 5: Collection Operations
// ❌ fromIndex > toIndex
list.subList(5, 2); // 💥
// ✅ Ensure correct order
int from = Math.min(a, b);
int to = Math.max(a, b);
list.subList(from, to);