Demo for optional methods.

Demo

import java.util.Optional;

public class Demo {
    class Person {
        private String name = "Hello To Optional";

        public Optional<String> getName() {
            return Optional.ofNullable(name);
        }
    }

    public void optionalMethodDemo() {
        Person person = new Person();
        /**
         * of() Example
         */
        Optional<Person> personOptional = Optional.of(person);

        /**
         * ofNullable() Example
         */
        Optional<String> dataWithNull = Optional.ofNullable(null);

        /**
         * empty() Example
         * Also (emptyOptional.get();)this will throw an Exception as get() only deal with value.
         * Not with empty Optional object.
         */
        Optional<String> emptyOptional = Optional.empty();
       // emptyOptional.get();

        /**
         * map() Example
         */
        Optional<Optional<String>> wrapper = personOptional.map(Person::getName);
        Optional<String> nameOptional = wrapper.orElseThrow(IllegalArgumentException::new);
        String name1 = nameOptional.orElse("");
        System.out.println("name1 :: " + name1);

        /**
         * flatMap() Example
         */
        String name = personOptional.flatMap(Person::getName).orElse("");
        System.out.println("name :: " + name);

        /**
         * isPresent() Example
         */

        if(personOptional.isPresent()){
            System.out.println("The Data isPresent :: " +  personOptional);
            System.out.println("The Data isPresent and the data is :: " +  personOptional.orElse(person).name);
        }

        /**
         * ifPresent() Example
         */
        personOptional.ifPresent(data -> System.out.println(personOptional.orElse(person).name));

        /**
         * filter() Example
         */
        Optional<Person> filterValue = personOptional.filter(data -> data.name.equals("Hello To Optional"));
        System.out.println("Filter value :: " + filterValue);
        /**
         * orElse() Example
         */
        String value = personOptional.orElse(person).name ;
        System.out.println("value :: " + value) ;

        /**
         * orElseGet() Example
         */
        String invokedValue = personOptional.orElseGet(() -> person).name ;
        System.out.println("invokedValue :: " + invokedValue);

        /**
         * equals() Example
         */
        Optional<String> data1 = Optional.of("knoldus");
        Optional<String> data2 = Optional.of("knoldus");
        System.out.println(data1.equals(data2)); // true
        System.out.println(data1 == data2); // false

        Optional<String> data1 = Optional.empty();
        Optional<String> data2 = Optional.empty();
        System.out.println(data1.equals(data2)); // true
        System.out.println(data1 == data2); // true

        /**
         * orElseThrow() Example
         */
        String notNullValue = personOptional.orElseThrow(IllegalArgumentException::new).name;
        String nullValue = dataWithNull.orElseThrow(IllegalArgumentException::new); //throw IllegalArgumentException
        System.out.println(notNullValue);
        System.out.println(nullValue);


    }
    public static void main(String []args){
        Demo demo = new Demo();
        demo.optionalMethodDemo();
    }
}