How can I evaluate next statement when null was returned in Java?

Question

How can I do something like the following JavaScript code, in Java?

var result = getA() || getB() || getC() || 'all of them were undefined!';

What I want to to do is to continue evaluating statements or methods, until it gets something instead of null.

I would like the caller code to be simple and effective.

Answer 1

You could create a method for it.

public static <T> T coalesce(Supplier<T>... ts) {
    return asList(ts)
        .stream()
        .map(t -> t.get())
        .filter(t -> t != null)
        .findFirst()
        .orElse(null);
}

code taken from: http://benjiweber.co.uk/blog/2013/12/08/null-coalescing-in-java-8/

edit As mentioned in the comments. Find below a small snippet how to use it. Using the Stream API has an advantage over using vargs as method parameter. If the values returned by the methods are costly and not returned by simple getters the vargs solution would evaluate all those methods first.

import static java.util.Arrays.asList;
import java.util.function.Supplier;
...
static class Person {
    String name;
    Person(String name) {
        this.name = name;
    }
    public String name() {
        System.out.println("name() called for = " + name);
        return name;
    }
}

public static <T> T coalesce(Supplier<T>... ts) {
    System.out.println("called coalesce(Supplier<T>... ts)");
    return asList(ts)
            .stream()
            .map(t -> t.get())
            .filter(t -> t != null)
            .findFirst()
            .orElse(null);
}

public static <T> T coalesce(T... ts) {
    System.out.println("called coalesce(T... ts)");
    for (T t : ts) {
        if (t != null) {
            return t;
        }
    }
    return null;
}

public static void main(String[] args) {
    Person nobody = new Person(null);
    Person john = new Person("John");
    Person jane = new Person("Jane");
    Person eve = new Person("Eve");
    System.out.println("result Stream API: " 
            + coalesce(nobody::name, john::name, jane::name, eve::name));
    System.out.println();
    System.out.println("result vargas    : " 
            + coalesce(nobody.name(), john.name(), jane.name(), eve.name()));
}

output

called coalesce(Supplier<T>... ts)
name() called for = null
name() called for = John
result Stream API: John

name() called for = null
name() called for = John
name() called for = Jane
name() called for = Eve
called coalesce(T... ts)
result vargas    : John

As shown in the output. In the Stream solution the methods returning the values will be evaluated inside the coalesce method. Only two are executed, as the second call returns the expected non-null value. In the vargs solution all methods returning the values are evaluated before the coalesce method is invoked.

Answer 2

If you really want to use java8 stream API, then look at the SubOptimal's solution.

In pure Java, you can't write the same line as in javascript: java will be more verbose.

If your getter is not time/resource consuming and you do not care about calling them twice, you can do:

String result = getA() != null ? getA() :
    (getB() != null ? getB() :
       (getC() != null ? getC() :
           "default value"));

Else you can do it with plain if:

String result = getA();
if (result == null) {
    result = getB();
    if (result == null) {
        result = getC();
        if (result == null) {
             result = "default value";
        }
    }
}