Make a java method return different objects in one single call

Question

I have a java method which has to return both List<ObjectA> and a List<List<String>> for each and every call made to it.

One way I can think of achieving this is by returning Map<String, Object> where string will be key and object will be my lists. But I think returning a Map is not an elegant way of doing so in my scenario. Any help with this?

Answer 1

With Java 14+, we have the possibility to use Records (JEP 395, openjdk.org). Without knowing anything of the semantics, I will demonstrate the usage with a generic record Pair, but we can of course always find more descriptive names.

We define a generic Pair of generic types T and U:

record Pair<T, U> (T first, U second) {}

And a dummy-implementation of ObjectA:

class ObjectA {
  private final String name;

  public ObjectA(String name) {
    this.name = name;
  }

  @Override
  public String toString() {
    return "ObjectA{" +
        "name='" + name + '\'' +
        '}';
  }
}

We can then implement our method like this:

public static Pair<List<ObjectA>, List<List<String>>> foo() {
  return new Pair<>(
      List.of(new ObjectA("one"), new ObjectA("two")),
      List.of(
          List.of("three", "four"),
          List.of("five", "six"),
          List.of("seven", "eight")));
}

And call it like this:

var fooResult = foo();
System.out.println(fooResult.first()); // prints the List<ObjectA>
System.out.println(fooResult.second()); // prints the List<List<String>>
System.out.println(fooResult);

This would produce the following output:

[ObjectA{name='one'}, ObjectA{name='two'}]
[[three, four], [five, six], [seven, eight]]
Pair[first=[ObjectA{name='one'}, ObjectA{name='two'}], second=[[three, four], [five, six], [seven, eight]]]

(Sorry, no Ideone.com demo, Ideone does not support Java 14+, only Java 12)