Java Optional Cheat Sheet
Category: Creation
Methods / Descriptions:
> Optional.empty() - Creates an empty Optional
> Optional.of(value) - Creates Optional with non-null value(throws if null)
> Optional.ofNullalbe(value) - Creates Optional that may hold null
Example:
> Optional<String> o = Optional.empty();
> Optional.of("Hi")
> Optional.ofNullalbe(null)
Category: Check Presence
Methods / Descriptions:
> isPresent() - Return true if value exist
> isEmpty() - Return true if no value
> Optional.ofNullalbe(value) - Creates Optional that may hold null
Example:
> opt.isPresent()
> opt.isEmpty()
Category: Conditional Execution
Methods / Descriptions:
> ifPresent(Consumer) - Runs code if value exists
> ifPresentOrElse(Consumer, Runnable) - Runs one action if present, another if empty
Example:
> opt.ifPresent(System.out::println)
> opt.ifPresentOrElse(System.out::println, () System.out.println("Empty"))
Category: Get Value
Methods / Descriptions:
> get() - Returns value (throws if empty) — avoid unless sure
> orElse(default) - Returns value or default
> orElseGet(Supplier) - Returns value or generates default
> orElseThrow() - Throws NoSuchElementException if empty
> orElseThrow(Supplier) - Throws custom exception if empty
Example:
> opt.get()
> opt.orElse("Default")
> opt.orElseGet(() -> "Generated")
> opt.orElseThrow()
> opt.orElseThrow(() -> new IllegalArgumentException())
Category: Transform
Methods / Descriptions:
> map(Function) - Transforms value if present
> flatMap(Function) - Like map but avoids nested Optionals
Example:
> opt.map(String::length)
> opt.flatMap(v -> Optional.of(v.toUpperCase()))
Category: Filter
Methods / Descriptions:
> filter(Predicate) - Keeps value if matches condition
Example:
> opt.filter(v -> v.startsWith("A"))
Category: Stream API
Methods / Descriptions:
> stream() - Converts Optional to Stream
Example:
> opt.stream().forEach(System.out::println)
Ex. All in One
import java.util.Optional;
public class OptionalCheatSheetDemo {
public static void main(String[] args) {
Optional<String> opt = Optional.ofNullable("Hello");
// Check presence
if (opt.isPresent()) {
System.out.println("Value: " + opt.get());
}
// Conditional execution
opt.ifPresentOrElse(
val -> System.out.println("Upper: " + val.toUpperCase()),
() -> System.out.println("No value")
);
// Transform
int length = opt.map(String::length).orElse(0);
System.out.println("Length: " + length);
// Filter
opt.filter(v -> v.startsWith("H"))
.ifPresent(v -> System.out.println("Starts with H: " + v));
// Safe default
String result = opt.orElseGet(() -> "Default Value");
System.out.println("Result: " + result);
}
}
Additional examples
Optional<String> opt = Optional.ofNullable("HELLO");
if (opt.isPresent()) {
System.out.println("Value: " + opt.get());
}
opt.ifPresentOrElse(
val -> System.out.println("Its not null"),
() -> System.out.println("It is null")
);
Output
Value: HELLO Its not null
✅ Pro Tip:
- Use
map+filterto chain transformations without null checks. - Use
orElseGetinstead oforElsewhen the default value is expensive to compute. - Avoid using
Optionalfor class fields or method parameters — it’s meant for return types.