Java 8 streams - filter by comparing two lists

Question

I have 2 lists which are different from one another

public class App1{
    private String name;
    private String city;

    // getter setter

    // constructors
}

public class App2{
    private String differentName;
    private String differentCity;
    private String someProperty1;
    private String someProperty2;

    // getter setter

    // constructors
}

List<App1> app1List = new ArrayList<>();
app1List.add(new App1("test1","city1"));
app1List.add(new App1("test2","city2"));
app1List.add(new App1("test3","city3"));
app1List.add(new App1("test4","city4"));

List<App2> app2List = new ArrayList<>();
app2List.add(new App2("test2","city2"));
app2List.add(new App2("test3","city3"));

As you see the App1 & App2 class are 2 different pojos having different property names, however the content/value that's held by name,city & differentName,differentCity property respectively is same i.e. test1, test2, test3 & city1, city2 etc

Now I need to filter app1List comparing names & city in other list i.e. app2List that doesn't exists.

final output would be

app1List.add(new App1("test1","city1"));
app1List.add(new App1("test4","city4"));

Easiest way is to loop one of the other lists multiple time which i am trying to avoid. Is there any way in Java 8 streams without having to loop multiple times??

Answer 1

You can make use of noneMatch operation, such as:

List<App1> result = app1List.stream()
        .filter(app1 -> app2List.stream()
                .noneMatch(app2 -> app2.getDifferentCity().equals(app1.getCity()) &&
                        app2.getDifferentName().equals(app1.getName())))
        .collect(Collectors.toList());

This assumes the combination of both name and city is matched while filtering.