orElse and orElseGet
- Java course
- Advanced
- Lesson 10/82
- 5 min
Learn default values with orElse and orElseGet.
Default value: orElse
orElse(default) returns the value if present, otherwise the given default. This is the simplest way to handle an empty Optional safely.
Example: opt.orElse("Guest"). If opt is empty the result is "Guest"; if not, the inner value is returned. One caveat: the expression passed to orElse is always evaluated, even when opt is present. If it is an expensive computation this is wasteful; for such cases orElseGet is a better fit.
Lazy default: orElseGet
orElseGet(Supplier) also returns a default value; but it produces the default lazily through a Supplier. The default is computed only when the Optional is empty.
Example: opt.orElseGet(() -> fetchFromDb()). If opt is present fetchFromDb is never called; if empty, it is called. This saves performance on expensive operations compared to orElse. Because a Supplier is a function re-evaluated on each call, it is also safer in code with side effects.
Practice Give a default to an empty Optional
Create an empty Optional<String> with Optional.empty(). Use orElse("Guest") to get the default value. Print the result with System.out.println.
Starter code
import java.util.Optional;
// Create an empty Optional
// Use orElse with "Guest" as default
// Print the resultSample solution
import java.util.Optional;
public class OrElseDefault {
public static void main(String[] args) {
Optional<String> name = Optional.empty();
String result = name.orElse("Guest");
System.out.println(result);
}
}Expected output
Guest
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Complete the orElse call
String result = opt.____("Misafir");String result = opt.orElse("Misafir");Explanation: orElse returns the default when the value is absent.
2 Match the orElse family
| Term | Meaning |
|---|---|
orElse |
Value or default |
orElseGet |
Takes a Supplier |
orElseThrow |
Throws an error |
orElse(default) |
Always evaluated |
3 Which method takes a Supplier for the default value?
- orElse
- orElseGet Correct answer
- ifPresent
- orElseThrow
Explanation: orElseGet takes a Supplier and produces the default lazily.