Introduction to Consumer Functional Interface

Interface Name	Description	Abstract Method
Consumer<T>	Accepts a single (reference type) input argument and returns no result	void accept(T t)
DoubleConsumer	Accepts a single double-value argument and returns no result	void accept(double d)
IntConsumer	Accepts a single int-value argument and returns no result	void accept(int i)
LongConsumer	Accepts a single long-value argument and returns no result	void accept(long l)
BiConsumer<T, U>	Accepts two (reference type) input argument and returns no result	void accept(T t, U u)
ObjDoubleConsumer<T>	Accepts an object-value and a double-value argument and returns no result	void accept(T t, double d)
ObjIntConsumer<T>	Accepts an object-value and an int-value argument and returns no result	void accept(T t, int i)
ObjLongConsumer<T>	Accepts an object-value and a long-value argument and returns no result	void accept(T t, long l)

accept(T t) is an abstruct method in Consumer functional interface. It takes input and return nothing.

It has only one default method called andThen(), which is used for chaining.

public class Applicant {
    private String name;
    private String email;

    Applicant(String name, String email){
        this.name = name;
        this.email = email;
    }
    public String getName() {
        return name;
    }
    public String getEmail() {
        return email;
    }

    public void processApplication(Consumer<Applicant> applicationProcessor) {
        applicationProcessor.accept(this);
    }
}

public class Main {
    public static void main(String[] args) {
        Applicant newApplicant = new Applicant("Alice", "alice@gmail.com");

        Consumer<Applicant> emailSender = (Applicant applicant) ->{
            System.out.println("Sending confirmation email to: " + applicant.getEmail());
            System.out.println("Email send successfully");
        };

        Consumer<Applicant> databaseUpdater = (Applicant applicant) ->{
            System.out.println("Updating database with applicant information: ");
            System.out.println("Name: " + applicant.getName());
            System.out.println("Email: "+ applicant.getEmail());
            System.out.println("Database updated successfully..!");
        };

        newApplicant.processApplication(emailSender);
        newApplicant.processApplication(databaseUpdater);

        // instead of above two line, we can use andThen() default method of Consumer Interface.
        newApplicant.processApplication(emailSender.andThen(databaseUpdater));
    }
}

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