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String Conversion

Converting between Strings, Numbers, and Dates in Java

Conversion Pipeline

Type a value in the input, then click a conversion method to see the result.

String value:
Choose a Method
Integer.parseInt()
Returns: int
Double.parseDouble()
Returns: double
Float.parseFloat()
Returns: float
"42"
→
method()
→
?
// Click a method above to see the conversion
Common Gotchas

Click each card to try the problematic input and see what happens.

Non-numeric text
"abc" → parseInt()
Letters cannot become numbers
Decimal with parseInt
"42.5" → parseInt()
parseInt cannot handle decimals
Empty string
"" → parseInt()
Nothing to parse
Extra spaces
" 42 " → parseInt()
Use .trim() first!
Remember: Scanner's nextLine() always returns a String. If you need a number, you must parse it!
int age = Integer.parseInt(scanner.nextLine());
Date Parsing with LocalDate

Java uses LocalDate.parse() with a DateTimeFormatter to convert strings into dates.

String Input
"07/15/2025"
→
Pattern
"MM/dd/yyyy"
→
LocalDate
2025-07-15
Pattern Breakdown
Formatter Code Reference
Symbol Meaning Example (July 5, 2025)
dDay (no padding)5
ddDay (zero-padded)05
MMonth (no padding)7
MMMonth (zero-padded)07
MMMMonth abbreviationJul
MMMMFull month nameJuly
yyTwo-digit year25
yyyyFour-digit year2025
Tip: ISO format (yyyy-MM-dd) is the default for LocalDate.parse(). For any other format, you must provide a DateTimeFormatter.
Converting Back to Strings

Click each card to see how it works.

Number to String (Option 1)
String.valueOf(42)
int → String
Number to String (Option 2)
Integer.toString(42)
int → String
Date to ISO String
date.toString()
LocalDate → String
Date with Custom Format
date.format(formatter)
LocalDate → String
Remember: Scanner's nextLine() always returns a String. If you need a number, you must parse it!
Tip: String concatenation with + also converts numbers to strings automatically:
String message = "Price: $" + 19.99;  // "Price: $19.99"

Click tabs to explore String-to-Number, String-to-Date, and reverse conversions.