import java.util.function.Consumer;
import java.util.function.Function;
import java.util.Optional;

public class Example {

    public static void main(String []args) {

        // Create a series of nullable objects.
        Test a = new Test();
        Test b = new Test();
        Test c = new Test();
        Test d = new Test();

        a.setInner(b);
        b.setInner(c);
        c.setInner(d);

        // This is probably as close as we're going to get to
        // null coalescing without actual language support.
        Optional
            .ofNullable(a)
            .map(i -> i.getInner())
            .map(i -> i.getInner())
            .map(i -> i.getInner())
            .ifPresent(i -> i.hello());

        // If you go too deep and find a `null`, nothing happens.
        Optional
            .ofNullable(a)
            .map(i -> i.getInner())
            .map(i -> i.getInner())
            .map(i -> i.getInner())
            .map(i -> i.getInner())
            .map(i -> i.getInner())
            .map(i -> i.getInner())
            .ifPresent(i -> i.hello());

        // You can also just retrieve a value instead of consuming the object.
        String string = Optional
            .ofNullable(a)
            .map(i -> i.getInner())
            .map(i -> i.getInner())
            .map(i -> i.getInner())
            .map(i -> i.toString())
            .orElse("<is null>");

        System.out.println(string);
    }

    private static class Test {
        private Test inner;

        public Test getInner() {
             return inner;
        }

        public void hello() {
            System.out.println("Hello, world!");
        }

        public void setInner(Test inner) {
            this.inner = inner;
        }
    }
}