The ifPresent method of the Optional class is an instance method that performs an action if the class instance contains a value.
This method takes in the Consumer interface’s implementation whose accept method will be called with the value of the optional instance as the parameter to the accept method.
To learn about the
Optionalclass, refer to this shot.
Optional classThe Optional class is defined in the java.util package. Use the import statement below to import the Optional class.
import java.util.Optional;
public void ifPresent(Consumer<? super T> action)
Consumer<? super T> action: An implementation of the Consumer interface.The method doesn’t return anything.
We create an instance of the Optional class in the code below using the ofNullable method. We create this class for different values and for the Consumer interface’s implementation that prints the value stored in the Optional instance.
To learn more about the
ofNullablemethod, refer to What is the optional class in Java?.
In the first example, we create an Optional object from a non-empty string. Hence, the Consumer interface implementation gets executed and prints the value stored in the Optional object.
In the second example, we create an Optional object from a null value. As the value passed is null, the ofNullable method replaces it with an empty Optional.
Hence, the Consumer interface implementation is not executed as the optional object has no value.
import java.util.Optional;import java.util.function.Consumer;class Main {public static void main(String[] args) {Consumer<String> stringConsumer = (s) -> System.out.println("The value stored in Optional object - " + s);String test = "hello-educative";Optional<String> stringOptional = Optional.ofNullable(test);System.out.println("When a value is present - ");stringOptional.ifPresent(stringConsumer);System.out.println("----------");test = null;System.out.println("When no value is present - ");stringOptional = Optional.ofNullable(test);stringOptional.ifPresent(stringConsumer);}}