How to all elements based on property that dont exist on another list

Question

I have two SETs fooSet and barSet of different objects foo and bar with properties:

Class Foo { String name, Integer age }

Class Bar { String name } 

I want to know ALL THE ELEMENTS of the fooSet where name does not exist in the barSet

I did multiple things but dont work. I don't know how to fix this issue

barSet.forEach(b -> fooSet.stream().anyMatch(f -> f.getName().equals(b.getName())));

Example:

[Foo: "Johnny", 28; Foo: "Travolta", 10; Foo: "Smith", 15]
[Bar: "Travolta"; Bar: "Smith"]

I want to get Johnny

Any help?

Answer 1

Those one-liners in the other answers are probably doing their job, but they are not necessarily readable. You could also instead do the following.

First, create a Set with all names of Bar, and then process all Foo objects:

Set<String> names = barSet.stream()
    .map(Bar::name)
    .collect(Collections.toSet());

Set<Foo> result = fooSet.stream()
   .filter(foo -> !names.contains(foo.name()))
   .collect(Collectors.toSet());

Answer 2

You want to search for each entry through the barSet and look if any entry matches the name from the Foo-Object or rather you want to remove the entry from the set when there is no entry in the barSet with the same name:

String name = "Johnny";
Set<Foo> foos = new HashSet<>( Arrays.asList( new Foo( name, 28 ), new Foo("Smith", 20 ) ) );
Set<Bar> bars = Collections.singleton( new Bar( name ) );
foos.removeIf( foo -> bars.stream().noneMatch( bar -> bar.getName().equalsIgnoreCase( foo.getName() ) ) );

Answer 3

You could filter the fooSet by removing all name that are not present in barSet :

fooSet.stream().filter(foo -> !barSet.stream().map(Bar::getName).collect(Collectors.toList()).contains(foo.getName())).collect(Collectors.toList());