Functional interfaces:
| Interface | Method | Return type |
|---|---|---|
Supplier<T> |
get() |
T |
Consumer<T> |
accept(T) |
void |
<BiConsumer<T, U> |
accept(T, U) |
T |
Predicate<T> |
test(T) |
boolean |
BiPreidcate<T, U> |
test(T, U) |
boolean |
Function<T, R> |
apply(T) |
R |
BiFunction<T, U, R> |
apply(T, U) |
R |
UnaryOperator<T> |
apply(T) |
T |
BinaryOperator<T> |
apply(T, T) |
T |
For setting development for Java 17, see https://stackoverflow.com/questions/70083274/java-17-java-invalid-source-release-7-with-enable-preview-preview-language/70083285#70083285
Use Supplier
package org.example; import java.time.LocalDate;
import java.util.function.Supplier; public class App { public static void main(String[] args) { Supplier<LocalDate> localDateSupplier = LocalDate::now; Supplier<LocalDate> localDateSupplier1 = () -> LocalDate.now(); LocalDate localDate = localDateSupplier.get(); LocalDate localDate1 = localDateSupplier1.get(); System.out.print("localDate = "); System.out.println(localDate); System.out.print("localDate1 = "); System.out.println(localDate1); } }
result
localDate = 2021-11-23
localDate1 = 2021-11-23
More complete object
ArrayList<String> stringArrayList = new ArrayList<>(); stringArrayList.add("Do Nhu Vy"); stringArrayList.add("Nguyen Bich Van"); stringArrayList.add("Nguyen Hong Do"); stringArrayList.add("Nguyen Tien Nam"); Supplier<ArrayList<String>> arrayListSupplier2 = () -> { return stringArrayList; }; ArrayList<String> strings2 = arrayListSupplier2.get(); System.out.print("strings2 = "); System.out.println(strings2);
or other way
Supplier<ArrayList<String>> arrayListSupplier2 = () -> { ArrayList<String> stringArrayList = new ArrayList<>(); stringArrayList.add("Do Nhu Vy"); stringArrayList.add("Nguyen Bich Van"); stringArrayList.add("Nguyen Hong Do"); stringArrayList.add("Nguyen Tien Nam"); return stringArrayList; }; ArrayList<String> strings2 = arrayListSupplier2.get(); System.out.print("strings2 = "); System.out.println(strings2);
result
strings = []
strings2 = [Do Nhu Vy, Nguyen Bich Van, Nguyen Hong Do, Nguyen Tien Nam]
How Java virtual machine manage object what is instance of Supplier interface? Try an experiment:
System.out.print("arrayListSupplier2 = "); System.out.println(arrayListSupplier2);
result
arrayListSupplier2 = org.example.App$$Lambda$19/_@.com
Implicity way, this is the result of arrayListSupplier2.toString() . Symbol $$ means object exist on memory only, not in hard disk. Exactly, arrayListSupplier2 initialized by a lambda expression as you seen in the below.
Implement Consumer interface
package org.example; import java.util.HashMap;
import java.util.function.BiConsumer;
import java.util.function.Consumer; public class SampleConsumer { public static void main(String[] args) { Consumer<String> stringConsumer = System.out::println; Consumer<String> stringConsumer1 = vy -> System.out.println(vy); stringConsumer.accept("Nguyen Bich Van"); stringConsumer1.accept("Tran Phuong Ly"); var map = new HashMap<String, Integer>(); BiConsumer<String, Integer> stringIntegerBiConsumer = map::put; BiConsumer<String, Integer> stringIntegerBiConsumer1 = (ke, va) -> map.put(ke, va); stringIntegerBiConsumer.accept("pigeon", 2); stringIntegerBiConsumer1.accept("pig", 4); System.out.print("map = "); System.out.println(map); } }
Result
Nguyen Bich Van
Tran Phuong Ly
map = {pigeon=2, pig=4}