Converting Between Strings and Other Data Types in Java

String conversion is a daily task for Java developers — whether reading user input, formatting values for display, or storing data. Java provides robust APIs for converting strings to/from primitives, objects, arrays, and more.

This tutorial explores every key conversion between String and other data types in Java, helping you write safer, more efficient, and more readable code.

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🔄 Why String Conversion Matters

• Reading from user input (Strings) and converting to numbers or booleans
• Serializing objects for logging, networking, or persistence
• Formatting output for reports or UIs

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🔢 String ↔ Integer

String to int

int num = Integer.parseInt("42");

int to String

String str = String.valueOf(42); // or Integer.toString(42)

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🔣 String ↔ Float / Double

String to float/double

float f = Float.parseFloat("3.14");
double d = Double.parseDouble("3.14159");

float/double to String

String s1 = String.valueOf(3.14f);
String s2 = Double.toString(3.14159);

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🔁 String ↔ Boolean

String to boolean

boolean b = Boolean.parseBoolean("true"); // case-insensitive

boolean to String

String str = Boolean.toString(true);

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🔤 String ↔ Char

char to String

char c = 'A';
String s = Character.toString(c);

String to char

char first = "Java".charAt(0);

⚠️ Ensure the string is not empty before calling charAt.

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📚 String ↔ Arrays

String to char array

char[] chars = "hello".toCharArray();

char array to String

String s = new String(new char[]{'J', 'a', 'v', 'a'});

String to String array (splitting)

String[] words = "one,two,three".split(",");

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🧱 String ↔ Objects

Object to String

String s = String.valueOf(new Date());

Java calls the object's toString() method.

String to Object (via parsing or custom logic)

int age = Integer.parseInt("30"); // Wrapper classes

Or use libraries like Jackson/Gson for object deserialization from JSON/XML.

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🕒 String ↔ Date/Time

String to LocalDate

LocalDate date = LocalDate.parse("2025-08-07");

LocalDate to String

String s = date.toString(); // ISO format

Custom Format

DateTimeFormatter fmt = DateTimeFormatter.ofPattern("dd-MM-yyyy");
LocalDate d = LocalDate.parse("07-08-2025", fmt);

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🧠 Performance and Safety Considerations

• Always validate input before parsing (e.g., try-catch for NumberFormatException)
• Use String.valueOf() over concatenation when performance matters
• Prefer toString() overrides for custom object conversion

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🔄 Refactoring Example

❌ Clumsy Conversion

String s = "" + 123; // works but not readable

✅ Clean Alternative

String s = String.valueOf(123);

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📌 What's New in Java?

Java 8+

• Optional.map(Object::toString)
• LocalDate, DateTimeFormatter

Java 11

• String.repeat(), isBlank()

Java 21

• String Templates (Preview) — improves conversion readability

String name = "Alice";
String msg = STR."Hello, \{name}";

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✅ Best Practices

• Use valueOf() or toString() for primitives and objects
• Always handle parse exceptions gracefully
• Prefer formatting APIs (String.format, DateTimeFormatter) for dates and decimals
• Validate input before converting strings to other types

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🔚 Conclusion and Key Takeaways

• Java offers simple, efficient ways to convert between String and other types.
• Always use appropriate APIs (parseXxx(), valueOf(), toString()) for clarity and safety.
• Choose formatters when dealing with locale-sensitive or custom-formatted data.

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❓ FAQ

1. What’s the difference between parseInt() and valueOf()?

• parseInt() returns an int; valueOf() returns an Integer (wrapper object).

2. Can I convert a String to a char?

Yes — use charAt(index).

3. How to convert boolean to String?

Use String.valueOf(boolean) or Boolean.toString().

4. What happens if I parse a non-numeric string?

A NumberFormatException is thrown.

5. Can I convert String to Enum?

Yes — use Enum.valueOf(MyEnum.class, str).

6. How to serialize an object to string?

Use .toString() or libraries like Jackson (JSON).

7. Is String.valueOf(null) safe?

Yes — it returns "null" string.

8. How to convert String to float?

Use Float.parseFloat("3.14").

9. How to parse date strings?

Use LocalDate.parse() or DateTimeFormatter.

10. Is String.valueOf(obj) better than obj.toString()?

Yes — it handles null safely.